September 22, 2008

What does that C-peptide test result mean?

PLEASE READ THIS ARTICLE CAREFULLY BEFORE COMMENTING OR EMAILING ME QUESTIONS ABOUT YOUR C-PEPTIDE TEST! The point of this article is that the C-peptide test tells you only if you are making some amount of insulin, but not how much. It cannot be used to diagnose ANYTHING unless it is very close to 0. People keep emailing me asking me questions that could be answered by reading this post in full.

Now back to the post:
One of the common questions I get from readers of my web site is what the result of a C-peptide test might mean and whether it can identify the kind of diabetes they have.

Unfortunately, in many cases, the answer is, that it cannot.

C-peptide is a chain of proteins that is spun off in the process by which the beta cell makes insulin. During this process, a precursor molecule, proinsulin is split into insulin and C-peptide. So for every molecule of insulin your beta cells produce, they also produce a molecule of C-peptide.

C-peptide is removed from the bloodstream by your kidneys while insulin is removed by the liver. This makes a difference in how long these peptides stay in the bloodstream. It takes half an hour until C-peptide is removed, while insulin is gone in five minutes. This means that there should be five times as much C-peptide in your blood at any given time as there is insulin and the longer activity period should smooth out the effects of testing at any one particular moment.

However, if there is something wrong with your kidneys they may not remove C-peptide in a normal manner and the result of a C-peptide test may be misleading.

If a person is injecting insulin, measuring C-peptide is the only way doctors can determine whether they are also making insulin on their own since lab tests do not distinguish between injected insulin and homemade.

Some doctors prefer to measure C-peptide even in people not injecting insulin because of its longer life in the bloodstream which means you won't see as much fluctuation from moment to moment in C-peptide levels as you may find with insulin levels.

The main thing a C-peptide test tells you is whether or not your body is making C-peptide. This sounds like a "duh" kind of statement. But in fact, that really is all that the test tells us. This can be useful in itself--if there is no C-peptide in a blood sample, your beta cells are not making any insulin. A very low C-peptide result is the definitive way to diagnose severe Type 1 diabetes--though many people with Type 1 will continue to have a low level of C-peptide in their blood for years after diagnosis as good control started soon after at Type 1 diagnosis appears to keep a small number of their beta cells alive.

To derive more meaning for the results of a C-peptide test the lab must know whether it was taken fasting or not fasting and what the blood glucose level was at the moment it was taken. In theory, a high fasting blood sugar with a high C-peptide value should point to Type 2 diabetes primarily caused by insulin resistance. That is because the high C-peptide value would suggest a lot of insulin was being produced but insulin resistance was keeping it from lowering blood sugar. In contrast, a C-peptide value that was normal or below normal taken at the same time as a high fasting glucose would suggest a form of Type 2 where failing beta cells rather than insulin resistance was the primary thing raising blood sugar.

In theory, testing C-peptide very few years should also give you some idea of whether or not your beta cells are slowly failing.

Unfortunately, it is here that things start breaking down. The problem is that there is no standardization in the way that labs measure C-peptide or in the reference ranges they provide. A recent study that sent 40 different samples out to 15 laboratories found nine different techniques being used. The study found that "Within- and between-run CVs [coefficient of variation (CV) equals the standard deviation divided by the mean (expressed as a percent).It is used to measure consistency across a range of results] ranged from <2% to >10% and from <2% to >18%,respectively."

In short, if you sent the same sample to a different lab, you could get a very different result. This study concluded this inconsistency was greatest, "...especially at higher C-peptide concentrations. Within-laboratory imprecision also varied, with some methods giving much more consistent results than others."

It is usually suggested that because of the different test protocols and reference ranges in use, you use the same lab to compare C-peptide values, when trying to determine if your C-peptide levels are dropping. But the results of the study above suggest that "within laboratory imprecision" is significant enough to make this a questionable strategy, too.

Labs may also not provide on a reference range for fasting C-peptide test results since most doctors order only fasting C-peptide tests. This can be a problem for those of us who have forms of diabetes where our beta cells are able to secrete basal insulin (the slow steady drip of insulin that keeps our blood sugar normal in the fasting state) but are unable to secrete insulin in response to the rising blood glucose that happens at meal time.

This pattern is characteristic of some forms of MODY diabetes, and explains why a person with MODY-1 or MODY-3 may have completely normal fasting C-peptide while experiencing extremely high blood sugars after meals. You can see an example of this in this MODY case history where the young patient whose genetic testing diagnoses MODY-1 has a normal C-peptide along with a 9.2% A1c.

With this in mind, here's what your C-peptide can tell you:

1. Very Low C-peptide test results.If your CC-peptide is significantly below the normal fasting range given by your lab no matter when your blood sugar was tested your beta cells are likely to be dead or dying. If you are young or very recently diagnosed with diabetes of any type, a very low C-peptide value is a good way of diagnosing Type 1 (autoimmune) rather than Type 2 diabetes.

But if you have had Type 2 for decades, and have not kept your blood sugars at normal levels, you may also have a very low C-peptide test value because over the years the very high blood sugars you have been exposed to may have killed off your insulin-producing beta cells.

Some insurers require a C-peptide test result below .5 nanograms/ml before they will cover the costs of an insulin pump.

2. High Fasting C-peptide Test Results. A high fasting C-peptide test value taken at the same time as a high fasting blood glucose test value suggests that you are insulin resistant though still making lots of insulin. (Unless you have kidney disease, in which case this test result may not reflect your actual insulin levels.)

If your fasting C-peptide level is high, it is very likely that you will be able to control your blood sugar by cutting way down on the amount of carbohydrate you eat.

It also means that you should first try strategies that lower insulin resistance before trying drugs that stimulate more insulin release, such as Amaryl, Glipizide, Januvia or Byetta.

If you have high fasting C-peptide levels, the drug Metformin, which increases insulin sensitivity, should be helpful in lowering your blood sugar. Exercise may also be very helpful as many people (though not all) find it temporarily reduces insulin resistance.

Weight loss may or may not help, depending on what is causing your insulin resistance. There are normal weight people who are very insulin resistant, but some people who are obese are able to reduce insulin resistance by losing weight--though of course, there is some circular logic here, since high levels of insulin resistance make weight loss very difficult!

3. Nonfasting C-peptide test results. If your non-fasting C-peptide test is not abnormally low (pointing to completely dead beta cells) there is no accurate way to interpret a non-fasting C-peptide test result. There are research studies where nonfasting C-peptide measurements are taken and studied, but given the nonstandarization of this test across labs and the fact that most labs do not give any lab reference range for nonfasting values, the meaning of a nonfasting C-peptide test that is normal or high (compared to a fasting reference range) is impossible to interpret.

If you have a normal C-peptide, very high post-meal blood sugars, normal or near normal weight, and a family history of thin people diagnosed with Type 2 diabetes or Type 1 diabetes that stayed relatively easy to control, you may have MODY but a C-peptide test will not be able to diagnose it.

Normal or High C-Peptide Test Results May Be Good News.

There is some recent research that suggests that C-peptide rather than being an inert byproduct of insulin synthesis is, in fact, important for preventing diabetic complications. This research is in its infancy. You can read about it in this earlier blog post.

If in fact it turns out that C-peptide is able to prevent complications, those of us who have secretory defects that respond to beta cell stimulation may have to reconsider whether or not to stimulate our beta cells with drugs like Byetta or sulfonylureas or whether to supplement with injected insulin that does not contain C-peptide.

I have been informed by correspondents diagnosed with MODY that they have been told by Dr. Hattersley who is one of the world's authorities on MODY, that he prefers to stimulate insulin secretion with gliclazide (Diamicron), a sulfonylurea drug that is unfortunately not available in the U.S., rather than use injected insulin because he believes it gives better long term results. If, in fact, C-peptide turns out to be beneficial, that might explain this finding. Unfortunately I have not been able to find any published research supporting the advantages of beta cell stimulation over insulin supplementation for people with MODY. The sulfonylurea drugs available in the U.S. often cause dramatic hunger and blood sugar swings that make them unpleasant to use and which lead to weight gain.

For people who do not have genetic secretory defects, the disadvantages of stimulating insulin secretion with drugs may be made clear by the most recent follow up to the UKPDS study, where people who used metformin to lower blood sugar had a far better long term outcome in terms of heart attack as those who used sufonylurea drugs. (Though all groups in this study had many more complications than necessary since they started out with A1cs of 7% or higher and allowed them to deteriorate over subsequent decades.) I'll be discussing this study in detail in a future blog post.


Jonty said...

This is interesting: Alpha-1 Anti-Trypsin, which is used to treat emphysema-like lung disease in adults and liver disease in children, resolves Type I diabetes in mice by acting as an anti-inflammatory.
I'm Type I of 25 years duration, but I'm going for a C-peptide test!

PRIVATE said...

I'm going to do a C-Peptide test and I believe it's called an antibody test as well. I'm taking Metformin but I still have to keep my carbs really LOW because I cannot tolerate carbs at all, even after my workouts. So if my C-peptide is low then my beta cells are dying or dead....what about the antibody test, what will that tell me ? Thanks.

Unknown said...

I just got a c-peptide 1.8
range 0.8-3.1 ng/ml
I'm type 2, does that mean I'm not all that bad off?

Jenny said...


That test result means you are making insulin, but not the huge amounts sometimes seen in Type 2s with a lot of insulin resistance.

PRIVATE said...

I'm confused. I just received a low c-peptide test plus low fasting insulin and a low fasting glucose. So does this mean that my beta cells are dying or dead ? I'm currently on Metformin.

Jenny said...

If your fasting glucose is normal, what those test results mean is only that you are probably not significantly insulin resistant and are making enough insulin to keep your blood sugar normal. This is good.

Jenny said...

High fasting blood sugars and low insulin and C-peptide means your beta cells aren't working.

High fasting blood sugars and high insulin means you are very insulin resistant.

C-peptide is really only useful for measuring whether you are making insulin of your own, as this blog post points out, it's not an accurate measure of anything else.

Unknown said...

I have lived with Type 1 diabetes for over 56 years.
Recently I read that some people living with Type 1
for over 50 years still produce very small amounts of
C-Peptide indicating that there could be an attempt
by the pancreas to regenerate. This is promising.
Assuming that the T-Cell responsible for damaging
the insulin producing beta cells could be suppressed,
could lead to at least a partial recovery of the islets.
On 4/04 my C-Peptide test results came back as <0.1
ng/ml. (ref. range: 1.1-4.6). I would like to retest using
a lab that can provide can provide an accurate calli-
bration down to a range between .01 and .1 ng/ml.
This would be useful in providing a reference start-ing point from which to measure against.
Any idea if a lab would have this capability and if so
where would I look to find one.
Thank You, Brian Robertson

Jenny said...

Brian, Because of how inaccurate the C-peptide test is, all it can tell you is whether or not you are making significant amounts of insulin or not. The exact measurement isn't reliable and as the study cited in this blog post found the same sample can yield different results if measured twice.

So unfortunately you can't get a good answer. If there ever is a way to regenerate what is left of pancreases, which there isn't now, they'll have to find some way to do this.

Beth Yannoulis said...

Can you please comment my test results:
Fasting Glucose 87
Insulin ranges from 13-15
C Peptide .9 (ref range .8-3.1 ng/ml)
a1c 5.8

I have been told that I am insulin resistant and pre-diabetic. BTW these #'s are while I am on a low glycemic diet.I have no family history and underweight (always have been). My only symptom has been problems with low blood sugar.

Jenny said...

Beth, Whatever you are doing seems to be working well for you based on the fasting blood sugar. But It's not possible to make a diagnosis from a single test results especially with insulin and C-peptide values which are, as this post tries to point out, not reliable on tests. And it's not my role to make diagnoses.

Unknown said...

I was diagnosed with pre-diabetes several years ago. My last A1C was 6.3. I am not on any diabetes medications.
I experience hypoglycemic reactions a couple of hours after eating breakfast (BS in the 40's). I recently had a fasting insulin and C-Peptide.
Results were: Insulin 35 uIU/ml (normal under 17). C-Peptide was 4 ng/ml (normal .8-3.1). My random glucose was 64. I read online that this may be caused by a tumor on the pancreas. My doctor referred me to an Endocronologist, who said that I didn't meet the criteria to be seen. Does anyone have any ideas? Thank!

Jenny said...

You need to talk this through with the doctor who originally referred you, as it's impossible to tell from your message what the endocrinologist's problem was.

tatiap95 said...

So newly diagnosed as a type 2 Diabetic. I was holding out hope for my husband that he was only insulin resistant and reducing maybe 20 pounds might significantly help him. However c-Peptide test just posted and it was 3.9 out of .9-7.1 his fasting glucose that day when they tested was 265. So does this mean his beta cells are damaged?

Jenny said...

All the C-peptide test in combination with the fasting glucose test tells you is that your husband is still making insulin, but not enough to lower his blood sugar to a safe level. It gives no information about what is causing the raised blood sugar.

Try the technique described HERE. It often works extremely well to lower the blood sugars.

The important thing right now isn't to speculate on causes, but to drop the blood sugar to a safe level. If the technique in the flyer doesn't help, demand aggressive treatment from your doctor. With a fasting blood sugar that high, your husband can't afford to delay. But give the dietary changes a shot first.

Unknown said...

I am a MODY 3 diabetic and just had a c-peptide done with a result of 1.0. What does this mean? My last A1c was 10.3. I just wore a continuous glucose monitor for a week and sugars were all over the place, even in the middle of the night.

Jenny said...


What it means is that like most people with MODY-3 you produce near normal normal fasting insulin. However, with MODY-3 you don't produce ANY insulin in response to the huge spike in blood sugar caused by the carobhydrate (starch and sugar) you eat at meals.

Fast acting insulin at meals (in low doses similar to what people use for Type 1 diabetes) can fix that. Prandin works for some people. Amaryl or glipizide for others, as long as all these oral drugs are used in very small doses. YOu need to find an endocrinologist who has read up MODY-3 as a lot don't know about it.

bhargav56 said...

Hi Vish here,

I am 27 years old i have taken the c- peditide fasting test i got the value as 1.32 ng/ml refence range (.9 to 7.1 ng/ml) fasting boold sugar was 95 Hba1c 5.7 as on sep 2010.
My was abnormal blood test was in agust 2009.
Fasting 120 mg/dl.
Post lunch 189 mg/dl
Hba1c 6.5

Can you tell me if i have type 1 or type 2 diabaties or is it pre diabaties.Please let me know if you need any more info.


Jenny said...

Vish, Your C-peptide result would tend to rule out Type 1 diabetes, and the rest of the numbers you report are technically pre-diabetes, but since pre-diabetes can produce the major diabetic complications given enough time, you'd be well advised to get those post meal blood sugars down into the safe zone--which is under 140 mg/dl.

flyingvan said...

I understand c-peptide isn't a marker for anything else. My wife gets all these neurological symptoms whenever eating or drinking (loss of vision, slurred speech, loss of balance, very mellow) No diabetes history and blood sugar remains constantly normal. Her c-peptide is 9.1 and pro insulin is 44.9. Why??

Jenny said...


Those sound like possible neurological problems. Has she seen an neurologist? Eating involves a lot of nerves including the vagus (master) nerve. Unfortunately, it is very hard to find doctors who know anything but the Top 40 diseases to diagnose something like that.

flyingvan said...

Thanks for replying so quickly. You are sure right about the 'Top 40' thing. We started with the neurologist; this whole thing began after she was hit in a car accident. Brain CT's, MRI's, EEG's before and during an episode, Neck soft tissue MRI's, carotid MRA's with and without contrast---all normal. The first abnormal thing we've found is the elevated c-peptide and proinsulin. I'm starting to suspect an insulinoma.....

flyingvan said...

Oh and we explored the vagus nerve option early on. Her signs and symptoms come with a spike in blood pressure so there isn't a typical postprandial hypotensive crisis. I guess the insulinomas are associated with catecholaminergic changes too though so we'll see...

Unknown said...

I need some help, and fast. I had a fasting t-peptide of 0.71 L, what ever does that mean, the nurse that called said, I had failed and did qualfy, for a pump. Please help me to understand what this means.

Jenny said...


What the nurse meant is that your test result showed you are making almost no insulin. This usually is interpreted as meaning you have a form of Type 1 diabetes. Most insurers will only pay for pumps for people with that diagnosis, not Type 2.

Unknown said...

Confused said...
What does it mean when someone has had a partial pancreatectomy and was placed on insulin. Blood glucose levels are now within normal limits but that is with use of both Lantus and Novolog. C peptide was done and is 1.3. Do you now start decreasing dose o Insulin or do you need to do more testing?

Jenny said...


This is something you need to discuss with an endocrinologist. The C-peptide test suggests you are making some insulin, but if your current doses of insulin aren't giving you hypos or causing you to wake up in the middle of the night with a pounding pulse (a reaction to a mid-night hypo), they may be exactly what you need.

Paula said...

i am 53. my islet cell ab was positive , islet cell ab titer was 640, gad65ab 13.8,glucose 73,c-peptide 0.4.
the dr. said i have diabetes type 1.5 or LADA.
did you ever hear of this?
i inject Lantus insulin 3 units at bedtime and Novolog insulin 2 units with dinner
what treatment is correct?
i am flipping out to say the least!

Jenny said...

Paula, Your doctor is a good doctor. LADA is a form of slow-developing Type 1 diabetes that strikes adults. Your treatment sounds like a good one to start. Over time, however, your insulin needs will probably change. You might find the book, Using Insulin, by John Walsh helpful in understanding how insulin is used. Once you understand how to match your insulin dose to your carbohydrate intake you may find that you get better blood sugars if you cut back on your carbohydrate.

If you learn how insulin works with blood sugar and how to adjust the dose to what you eat, you will be able to keep your blood sugar in the low, safe range that prevents complications.

The book, Dr. Bernstein's Diabetes Solution is also very helpful. With some of the modern insulins (Lantus,, Levimir, Novolog, Apidra) that Dr. Bernstein does not use it is possible to eat more carbohydrates than he recommends, but his book explains many concepts in ways that are very helpful.

Chitra said...

hello..i was diagnosed diabetic on 1st may 2011,,with FBS 270, PPBS 400..immediately started with low dose insulin..later got c-peptide test done which came out as 1.18 (ref range:1-7).so the doc increased insulin doses to 20(morning) and 12(evening)+ vildagliptin and acarbose tablets..the dose was later reduced to 10 and 4 bcoz of many recent hypoglycaemic attacks..aftr 25 days i repeated the c-peptide test and now it was 1.57. please tell me wat does this signify? is this increased value because of the human insulin (mixtard) injections i am taking or does c-peptide level only indicate insulin production of our body?? is it confirmed that i am a type 1 diabetic?? as my doc said this might b a stage of glucotoxicity. also my doctor is trying to slowly reduce the insulin doses n switch on to allopathic medicines (i'v also started with homeopathy). is it possible that i can live without insulin injections ever?? and wat if my c-peptide levels are normal once again (3-4)does that mean am not diabetic any more....??? please guide me..
Thank You.
Chitra A (India)

Chitra said...

i am 23yr old, female
Chitra A

Jenny said...


The point of this post and the study it cites is that the value of the C-peptide test means nothing because the test is so inaccurate that a variation like you describe can be entirely due to chance. All the test means is that you are making SOME insulin. It doesn't tell how much. But because you are making some, you probably are NOT a Type 1 diabetic.

katyb said...

My 5 year old son had recent symtpoms of onset of Type 1. (Frequent urination, exessive thirst and an initial blood result on a glucomiter of 165. Then he did fasting glucose which was 91 and a HA1C - normal but his C-peptide was low. We are painfully waiting results from medical conslutations. Can you give any info on what this might mean?

Jenny said...


I'm afraid you're going to have to wait and see what the doctors tell you. If they say he's fine, let's hope they're right. But keep testing, because sometimes these things take a while to become clear. I hope he's fine, though.

MilanM said...

I was diagnosed with Diabetes in May. I had a blood sugar of 12.3mmol/L, with HbA1C of 8.5%, c-peptide was 1.58. I was immediately given insulin, 4 units of bolus pre-meal, and 8 units of bolus before sleep. In the last 1.5 months i have reduced dosage to 1 unit of bolus pre-meal and 1-2 units of basal, with BG levels now ranging from 4-7mmol/L with minimal or no exercise at all. I have tried not to take insulin for 2 days, eating carb rich meals, like pizza, with a resulting max blood sugar of 8.5mmol/L. Can you give me some insight on my situation if possible, i live in a poor country with a terrible health care system, for 10 days i have spent in the hospital i have seen my doctor once for 3 minutes, only thing he said is that i`m "doomed" for life, i have no faith in them, none.

Jenny said...


It would be highly irresponsible for anyone to attempt to advise a stranger based on so little information. On the Blood Sugar 101 web site you can make a start at educating yourself about what is going on in your body, and there are several other useful books you'll find cited on our resource page.

The one thing I can say is that there is NO reason you shouldn't recover normal health if you study what is available online. All forms of diabetes can be controlled.

From the small size of the doses you are taking it sounds like you might have a form of autoimmune (Type 1) diabetes, in which case you might want to connect with other people diagnosed with Type 1 diabetes who you can find on forums and sites like They can give you tips and pointers that will also be helpful.

Nrmn said...

hi Jenny my C-Peptide is 1.53 ng/ml....(0.9-7.1).My sugar level usually remains low i.e. from 45-60...and sometimes normal..but usually after two to three days i have hypoglycemia..and my bp also remains low..i.e. 80/40...I have problem in remembering things and events...could you plz suggest me something...thanx

Nrmn said...

these are my fasting range of I have headaches frequently in morning..& tiredness when i getup in takes around 10-15 minutes for me to getup from bed..kindly tel me where these symptoms are leading to..?

Jenny said...


There is no way to know what is causing your problem based on your c-peptide test result. If you are taking insulin or a drug that stimulates insulin release like glipizide or glimiperide you need to talk to your doctor about lowering the doses (or changing the drugs you are taking) to avoid those lows.

If you aren't taking insulin, then you need to discuss the hypos with a capable doctor to diagnose the problem.

Nrmn said...

kindly tel me whether these c peptide result is normal ?
I am not taking any drugs or insulin or any such thing ..I have family history diabetes..

Jenny said...

If you read the article you commented on you would have learned that all the C-peptide test shows is whether or not you are making insulin. Not whether you are making normal amounts of it. You are making insulin.

You really need to see a a good doctor to learn why you are experiencing those lows.

Wendy said...

I have a general questions. I have T2 diabetes, and long story short, I have a very strong family history, with my father having died from complications of T1 and also my mother has an autoimmune disease, temporal arteritis. I am experiencing a change in my insulin needs. I have been trying to get my doctor to run the C-peptide and antibody test on me for baseline purposes. I get shot down by them, and I do understand why, especially after reading your informative article. If I am willing to pay for it, and I understand the variability of results, and I still "behave myself" and do what the doctor says, then why would a doctor not want to go ahead and order these results? It boggles my mind that a doctor would not want to know any and all information that is available to them about a patient.

Jenny said...


I wish I knew why ignorant doctors defend their ignorance so strongly. With your family history you should be tested for islet antibodies and C-peptide.

My own experience with resistant doctors--who are gatekeepers refusing services--is that sometimes you have to fight for what you need, pitch fits in the office, change doctors if you can, or appeal to your insurer.

An endocrinologist would be the best doctor to see if you can, but I know they can be hard to find in many parts of the country.

Kathy W. said...

Wendy, if you are willing to pay for your tests yourself, you can order them online at places like, which subcontract with your local LabCorp. You go to LabCorp or another local lab to get the tests done with a requisition you print out. You receive the results in a secure email link, often faster than if you'd had them done through your own dr. And the tests are often cheaper than self-paying through your dr.

I've used several of these online lab services to get c-peptide & other results.

Wendy said...

Jenny and Kathy, thank you so much for your responses. I had no idea about the ability to get the tests on my own! BTW, I am on tudiabetes under sparkysmom, and I posted a very interesting discussion about this very frustrating process and my history of diabetes if you are interested in reading about it. I WILL get these tests performed. I am going to my PCP next week and she is a wonderful doctor who I feel sure will order the tests for me.

strange labs said...

I am T2 for 14 yrs, on insulin pump. My insulin requirements with the pump have went from 150-200 units a day to 75 units a day. Blood sugars have dropped from 200-400 to around 100 with hypo events. My A1c dropped almost 2 points in 3 mo. My c-peptide was 12.5 with a 127 sugar. Any thoughts?

Jenny said...

Strange Labs,

What does your doctor who ordered the test say? All the C-peptide test tells me is that you are making some insulin on your own.

maggie said...

I have very low insulin (near or less than 1) and c-peptide (less than 1) consistently, yet normal glucose levels. I am thin, exercise a lot, eat a low glycemic diet that includes lots of protein. If I don't adhere to this lifestyle I have trouble w/ hypoglycemia & generally feeling horrid.
Could I be developing Type I diabetes. Any insight? should I be testing my blood glucose frequently?

Jenny said...


It is very unlikely that you are developing Type 1 diabetes. A low fasting C-peptide with normal blood sugar can be completely normal. As this article argues the ONLY time the C-peptide is informative if there is almost no C-peptide along with a high blood sugar.

If your sugar is normal, the body isn't going to be pumping out insulin. The C-peptide only shows that it has made insulin in the last few minutes. It's when the body NEEDS insulin--with blood sugars well over 120 mg/dl but none is being made that you have an indicator that the beta cells are failing.

maggie said...

Thank you for your insight; it is very much appreciated!

Alison said...

I did not fast before my c-peptide test and actually ate a nutri-grain bar on my way to the test. The result came back at 4.18 and my doc is extremely worried. She never told me to fast and in fact this test was accidentally run in substitution for a testosterone test. So because I didn't fast, could that have caused the high result because I ate something pretty starchy before testing? I'm so confused and worried! Please help!

Jenny said...

The range given for the C-peptide test is for a fasting test. So yes, if you had just eaten something that caused you to secrete a burst of insulin you could have a lot more c-peptide than you would fasting and be normal.

I'm really started to wonder why ALL the comments and email I get about this post seem to ignore the point it makes. The actual value on your C-peptide test rarely tells you anything more than that you are either a) making or b) not making insulin. The quantities are NOT diagnostic beyond the "yes, insulin is being made, and "No it isn't" level.

Alison said...

Well I am very UN-educated about this kind of stuff! I have no family history of anything abnormal, I am thin and young and have never had a problem with my insulin levels and thought it was VERY odd for me to get such a negative reaction from my doctor with these results. I told her I didn't fast and she didn't seem to think I needed to, but it seems like it would make all the difference in the world! I appreciate the feed back and am relieved to read on here that non-fasting levels, as long as they are normal or high is a good thing. I am going to get a second opinion and actually fast and see what my levels are then!

Jenny said...


The only test which gives a truly informative result is the one you can do at home with a blood sugar meter after you eat.

If your blood sugars stays under 140 mg/dl one hour after eating, you're normal. If it goes over 200 at any time within 2 hours you have diabetes. If it is over 140 mg/dl by 2 hours after eating it is pre-diabetes by the definition the doctors use, but already high enough to do damage to your organs.

Most of us who want to stay healthy try to keep blood sugar under 140 mg/dl as much as possible.

Unknown said...

Hi Jenny
My family has a long list of Type 2 diabetes members. I always watch out for that. This year I am start to hit line with a morning fasting 102.
Since then My fasting glucose is range between 89-102. my a1c is 5.2 to 5.4, my fructosamine is 202-206, in last 6 months I check every month. I have been home monitoring my post meal, it never go over 130(50 gram carb per meal).

However 2 days I did a fasting insulin test it come out <2UIU/ml (4-29 standard range) with a fasting glucose 99.

Is that indicate I might going to have Type 1 instead of type 2. I am lean and excericse a lot.

Should I ask the doc for a C-peptite test? They have refused to that for me. I always think I might end up with Type 2 but looks it is type 1 that is coming.

Jenny said...

As long as your fasting glucose is still in the normal range, which yours is, a low fasting insulin test in the range yours was in is also normal.

The fasting insulin test only points to Type 1 when the fasting blood sugar is very high.

You are right to keep an eye on your blood sugar, but it looks like what you are doing is keeping everything under control.

If your fasting gets well above 125 and you were still seeing very low fasting insulin the test you would ask for would NOT be the C-peptide, which as this blog post explains is a very poor test that is not informative.

To rule out Type 1 you would ask for islet and GAD antibody tests.

annegb said...

I'm not diabetic, nor has anyone in my family ever been diabetic. However, my blood sugar has been pretty up and down the last few years. Recently it's fallen rather dramatically at times, so my dr. had me take a c-peptide test, wondering about an insulinoma. The result is 3.5. There are a couple of other tests he did that haven't come back yet. I'm pretty scared now. I've never worried about this sort of thing before.

erica said...

My daughter was diagnosed with insulin resistance almost 2 years ago. She has been taking metformin since. Her labwork 6 months ago showed glucose at 85 insulin 20 and c-peptide 4.5, she has been exercising and trying to watch her diet, but recent labs(on an increased dosage of metformin) are as follows glucose 87, insulin level 28 and c-peptide 4.47. We saw he MD today and she doesn't have an answers as to why things aren't improving. She basically said she doesn't know what else to offer us. My daughter is overweight, and almost unable to lose any weight. Her numbers scare me. Anny thought? she is 16 years old

Jenny said...

Has your daughter been diagnosed with PCOS? It often causes the kind of insulin resistance you are describing. PCOS can be tough to treat. I have heard from some people diagnosed with it who did very well on a very low carb diet, so if your daughter hasn't given an Atkins style diet a good try (and hung out on one of the low carb diet support groups to get help with the problems that come up early on which aren't addressed in the diet books), that might be one approach to try.

Dr. Bernstein in his book, Dr. Bernstein's Diabetes Solution says that sometimes even the low carb diet doesn't work well. He talks about various other drugs he's used and gives the impression that sometimes they work and sometimes not. I know that spironolactone is one that is sometimes used, too.

You definitely need to find a doctor who is aware of how to treat PCOS if that is the case. This page talks about how to find a doctor who is experienced with treating PCOS: Searching for help on PCOS turns up a lot of scammy sites with people selling crap supplements etc. I have never heard of any supplement that will help this kind of problem, so stick to mainstream sources of help.

Natalie said...

Just because I'm approaching Medicare age, I decided to have a C-peptide done, so that I would know if they would cover my pump. Fasting C-peptide turned out to be 0.9 (normal 1.1-4.4) and within Medicare guidelines. So it seems this turns out to be too high for a Type 1 diagnosis, but not a typical Type 2, either, because with a BMI of 23.7, and TDD of insulin between 25 and 30 depending on what I eat, I don't seem to be really insulin resistant, either? Do you think it could be some kind of MODY? I read your MODY article, and I don't entirely fit in that box, either, but am curious whether I'm closer to that than anything else. (Or maybe I'll just stay Type Weird!)
Natalie ._c-

Jenny said...


It's more likely to be LADA, the slow autoimmune form of diabetes, particularly if it progresses over time. Do you have any other autoimmune conditions?

Unknown said...

I am really worried, I just had a C-peptide test done, I went to the hospital and picked up my results myself.

I was 10 hours fasting

BS: 306
CPep: 1.5
A1C 10.0

I take 90u Lantus and 30-50u Novolog with each meal... Very insulin resistance..

No one can tell me what to do, am I type 1 or 2? I feel like I am dying. I cant get in to the dr for another 2 weeks..

Godsfaithfulgurl said...

My doctors have tried to figure out for years(diagnosed at 19, now 36) what to do about my diabetes. I am now taking levemir and novolog along with maximum doses of metformin and actos and i am already having complications such as gastroparesis. My c peptide was 1.37 with a fasting of 132 because i had taken 60 units of insulin 2 hrs earlier and typically run high fastings in the 300-400 range. Can you tell me anything? My doctor was checking to see if I am type 1 or 2 but he has been out of the office and i was curious as to your opinion. Thank you.

Jenny said...


The C-peptide result looks like you are most likely a Type 2 no longer making much insulin, but you are making a small amount, unlike a Type 1.

Have you tried cutting back on your carbohydrates? Go to a site like and enter in what you are eating. You'll see what foods have the carbohydrates in them.

Start cutting back on the foods that have the most carbohydrate, a bit more at each meal. When you cut back, one hour after eating test your blood sugar with your blood sugar meter and you should start seeing the numbers come down.

If that doesn't help, you need to see an endocrinologist who can help you with your insulin doses. Some people need more than you are using. But before you do that, do try cutting down your carbohydrates.

Jenny said...


What you describe could be a rarer kind of diabetes that needs to be evaluated by a really good endocrinologist practicing out of a major regional teaching hospital affiliated with a good medical school. If there is any way you could see that kind of endocrinologist it would be worth doing, because the kinds of doctors that practice at community hospitals, including endocrinologists, don't have the training to deal with these rarer forms of diabetes, which may be what you have. There is a lot more to diabetes diagnosis than Type 1 and Type 2.

If your doctor can't help you, demand a referral to that kind of specialty medical-school associated clinic.

Sunny said...

I have undergone fasting C-Peptide tes. which is as...c-peptide 1.08 range 0.78-5.19, Fasting blood suger 116mg/dl.My age is 59 I am on oral diabetic medications VIZ metformin, vildagliptin, gliclazide,pioglitajone. What is my situation And what I have to do.

Satish Bhatnagar said...

I am 59 years my C-Peptide is 1.08ng/ml, fasting is 116mg/dl.I am type-2 diabetic.Taking oral medication (not taken insulin yet. my pp and random ssuger is always between 220-160.Where I stand please tell me.

Jenny said...


As this post explains, all that result tells you is that your body is making some insulin, but looking at your fasting blood sugar and all those meds, not quite enough.

Have you tried the strategy described here: ? Many people find it helps them not need so many drugs.

If that doesn't help, why not ask your doctor to put you on injected insulin, because you are taking so many drugs that are new, not really understood, and likely to have dangerous long term side effects. Insulin is much safer.

sandy said...

I have had 2 c-peptide tests to qualify for a pump, and they were both too high. I will be having another test. Is there anything I can do to produce a lower amount so I can qualify?
thank you

Jenny said...


If the criteria include a fasting glucose test along with a C-peptide test, probably not, because you'd need high fasting blood sugar along with a very low C-peptide to meet the specification which is that you be basically producing no insulin.

You can lower your insulin secretion by cutting back on carbs but that also lowers the fasting glucose, and, if you have Type 2, probably won't drop the C-peptide into the very low range characteristic of Type 1.

sandy said...

thank you. i have to have a fasting sugar of 225 or less along with a low c-peptide to qualify. if my sugar is too high, would taking some insulin before the test be ok. i am very insulin resistant.

Jenny said...


Are you sure it isn't 225 or MORE? Most insurers who limit pumps limit them to people who have extremely high blood sugars without injected insulin.

I don't know what the effect of injecting insulin would be. The c-peptide only measures how much insulin you are secreting. If you inject, you might secrete less, but it's hard to say. But it would also lower your fasting insulin, and I'd be very surprised if they'd give you a pump with a low c-peptide and normal fasting blood sugar since that, too, can happen to normal people.

If you need a lot of insulin, another solution is U-500 insulin which is highly concentrated so one unit does the work of 5, and in some people this will drop the dose needed dramatically (more than 5 times). Well-trained endocrinologists sometimes prescribe this for people with Type 2 who are extremely insulin resistant. It might work better than a pump.

sandy said...

wow, thank you so much.

I never heard of that kind of insulin. I have been on many and can only tolerate Apidra and Levemir. but it still takes 3 hours to bring my sugar down, but never to the normal level. The more insulin i take the higher my sugar stays and makes me retain a lot of water. I have the best results if i take between 30-50 u Apidra. if i take less or more my sugar goes up to 400 at times.

Jenny said...


Have you seen an endocrinologist who practices at a regional teaching hospital (vs one who is associated with a small local hospital?)
They are often more expert in treating difficult cases.

The quality of endos varies dramatically. The big regional teaching hospitals are pickier about the quality of doctors who practice there than small local hospitals, which in my experience are too frequently the homes of doctors who have "retired in place" and who have stopped learning anything that can't be explained in a one paragraph summary (helpfully provided by drug salespeople.)

U-500 insulin is a form of R (regular human) insulin. It's not branded the way the newer analog insulins are.

I learned about this treatment from a correspondent who was extremely insulin resistant and was prescribed the U-500 by a doctor at Stanford.

It is also used for a year or so when people have developed the rare insulin allergies which can drive up their insulin resistance dramatically.

tbass said...

I was diagnosed July 2011. wieght loss and symptoms. orig A1c 14.5 put on insulin and orals, but was going "low" with very low dosaes of insulin, so I stopped taking the insulin. I am down to a 7.4 Aic and had a non fasting
c-peptide of 1.76 (.8 scale) had a high 58. glut acid test (.5 scale), this test was done after i was on insulin therapy for 3 months or so. what can you tell me about my c peptide results, and what does the glut acid results mean? I've changed my diet significantly, but even a half a bagel raises my blood sugar considerably.

Jenny said...


All that C-peptide test shows is that you are making insulin. As the blog post here explains, this is a crude test that is not particularly informative. If there is basically no C-peptide, the person has dead beta cells (and often Type 1 diabetes) but beyond that the reading is not that informative.

The GAD antibody test is meant to determine if you have the antibodies that point to slow onset autoimmune diabetes, often called LADA. You can read the details HERE.

You'd need to discuss the result with the doctor who ordered the test to get the definitive interpretation of your result.

How low were you going on insulin? Often you will feel low at normal levels if you have been running high for a while which you were, based on that extremely high A1c. Unless you were seeing readings below 70 mg/dl, you were probably having "false hypos" which should go away as your body adjusts to normal readings.

If you were getting real lows, you probably want to study insulin dosing, to make sure you weren't prescribed a generic regimen. Books like Using Insulin by John Walsh or Dr. Bernstein's Diabetes Solution go into some detail about how to set doses.

A last resort is to try a different insulin. I found Humalog caused me hypos, but the same doses of Novolog did not. Some people do well on Apidra, too. Not all doctors understand that these insulins are different. Ditto you could try replacing Lantus with Levemir.

But first you need to talk to the doctor to find out what the interpretation of that GAD antibody test is. If it points to LADA, you will need to take insulin eventually, perhaps in very small doses, carefully managed.

Joan said...

So last summer I had a fasting c-peptide done and it was 0.8 (range 1.0-4.?) and my fasting bgl was 75 (range 75-?). I take 28 units Lantus and 1000gm Met twice a day and do a strick LC/HF diet (less than 20 gms of carb a day). A year before my c-peptide was 3.4 and bgl at the time was 95 (on same meds and diet). Is the low c-peptide along with lower average bgl mean I just don't need the insulin so it isn't secreting? Or I am taking too much Lantus? I have been trying to figure this out for a long time.

Jenny said...


There probably isn't a cut-and-dried answer to this question. Usually a C-peptide that low is interpreted as meaning your beta cells aren't functioning. People with Type 2 diabetes who are injecting insulin usually have normal amounts of C-peptide on a fasting test. In fact, having a C-peptide level that low is what will qualify you to get a pump on many insurance plans, but many Type 2s who inject insulin can't qualify because they never have C-peptide levels that low.

But who knows? This article suggests that it is a mistake to read too much into a C-peptide test.

You fasting bg is low enough that it probably wouldn't hurt to dial back the Lantus a little bit. But with that very low C-peptide it probably would be a mistake to stop it.

amy said...

Hi... Boy these comments and posts are helpful. I am a patient that has had autnomic neuropathy symptoms for 3 yrs, which were manageable and tought to actually be carcinoid syndrome instead for a while. I am now seeing a doc who thinks that it was diabetes/metabolic syndrome the entire time. In Dec. my FBS was 219, my 1 hr PP was 79... Haha (so weird) and my C-peptide was 2.1 ...also had a lot of assessment looks of a diabetic to my doc (scleroedema, tight tendons in feet/hands, swollen fingers and face), but weight 143 @ 5ft 8in. My HgbA1c was 5.5. In March i was starting to have peripheral neuropathy symptoms and my my C-peptide had gone up to 3.3, but no FBS was done. I finally bought my own BS equipment and started testing.. I have had mostly 89s and the range of BS have been 78-98 with one outlier of 128. I am losing more weight and am now 139 and my peripheral neuropathy is increasing and is obviously small fiber neuropathy. My doc will not come down on any real specifics of my "diabetes" and he is very unaccesible as he is a bigtime "expert" and is always touring about with lectures and his nurse is not very useful...sadly. I'm confused and wondering if any of this makes any sense to anyone else. Do you have an opinion on this? Confused in Va- Thanks

Jenny said...

A FBS of 219 would be very diabetic and high enough to cause neuropathy. If you have cut back on the carbs since then, and normalized your blood sugars, that would make the neuropathy more painful for a while because your nerves would be growing back. Eventually they heal. But if you're still eating the same foods as before and getting those numbers, then the very high FBS seems odd, and you should get a new test. The C-peptide only tells you that you don't have autoimmune diabetes that has destroyed your beta cells. However, if you have been taking cortisone or prednisone, that could cause the very high blood sugars too, no matter what your weight. And those high numbers could damage your nerves.

Keep the sugars down, though and they should get better over time.

amy said...

Thank you! I have decided to gluten-free, sugar free, and carb low..have also come off of Topamax as I was on it to help with these issues, but i think it may have made my B12 level low. If I take a vitamin B12, my pain level decreases significantly and if I don't it's bad. My question is about the 1hr post-prandial. How could it be so low. It was done on the same morning as the FBS of 219. Basically, had the FBS 219, was told to go out and eat a carb meal. I went and had two biscuits with sausage gravy, and my 1hr PP was 79. Any ideas? Thank you for this board...this means so much! -Amy

Jenny said...


It's possible that eating something caused your pancreas to secrete a big dollop of insulin. There are two different, not particularly related ways in which the pancreas secretes insulin. You can read about them here: How Blood Sugar Control Works.

andie said...

After reading this article and reading the comments, I'm very concerned. The results of my c peptide were high but my fasting glucose was normal and HgbA1c was 5.1 and the endocrinologist is starting me on Metformin??? Do I get an second opinion???

Jenny said...


If you are insulin resistant, which is what a very high C-peptide might point to, metformin is the appropriate treatment. It's a very safe drug.

Unknown said...


Three years ago my husband was diagnosed with type 2. We didn't take it very seriously for the first 2 years - (and the dietician's advice didn't help much either) cutting back somewhat on carbs. However for the past year we have been extremely serious - gone very low-carb (under 30 per day) - with non-starchy vegetables the only source of carbs. He is also on a minimal dose of metformin. In 6 months we dropped his A1c from 9.5 to just over 6. But it is a constant struggle to keep his glucose readings in the low 100's with it occasionally up around 120. We have never been able to get it into double digits.

He is due for his next 6 month checkup/blood work and we wondered if he should get either the c-peptide or GAD test. Also, I thought I read somewhere that he should carb load for a few days before the test as his diet is so low carb that there isn't any call for the body to produce insulin. Do you have any opinion on this? Thanks so much for this site - it is where we learned to test everything that he ate to check the effect on BG.

Jenny said...

The C-peptide test is only useful if you have some reason to think that your husband has an autoimmune form of diabetes. It is common for diet alone not to be enough to control blood sugars in Type 2. Metformin would be the next step and might make it possible to eat a bit more carb and still get good numbers.

You probably wouldn't need to think about C-peptide tests or antibody tests unless metformin had no effect and blood sugars started to rise even with a low carb intake.

If you do take a c-peptide test it wouldn't be necessary to carb up. That only applies to the glucose tolerance test. The body still makes insulin even when you eat a very low carb diet--people with Type 1 who eat low carb diets still have to inject both basal and bolus insulin or their blood sugars will rise to dangerous heights even eating low carb.

Unknown said...

Maybe he should ask to try a higher dose of metformin. Your liver will make extra sugar and metformin helps that.

Luv Nijhawan said...


My 11-months old son was diagnosed with diabetic ketoacidosis on 98 June 2012.

Since then we have been giving him basal and boluses in varied quantities depending upon his pre-and-post meals blood sugar levels (which are fluctuating between 32 and 486 mg/dL).

We also got his C-peptide tested which came out to be extremely low at 0.01 (normal lab range 0.48-3.36). Could you suggest if this is sufficient to confirm type 1 diabetes?

Also, three antibody tests are under process (Islet cells, insulin auto and GAD 65). Could you throw some light on the favorable results for these tests (basically we are praying and hoping that this might turn out to be a case of neonatal, transient diabetes; hence, please let me know in your view if a) that's a possibility, and b) what should these tests indicate in that scenario?)

Luv Nijhawan, New Delhi

Jenny said...


So sorry to hear of your son's challenging situation. That C-peptide is low enough to diagnose Type 1 diabetes. It sometimes takes a while for the antibodies to rise to detectable levels after an autoimmune attack, so it is not possible to conclusively diagnose your son right away, but if there are antibodies it would point to Type 1.

If not the transient neonatal diabetes is a possibility. In either case, the treatment would be the same, especially since the transient diabetes can return so it would be important to monitor blood sugars.

There have been many advances in the treatment of Type 1 over the years and people who develop it can do much better than they used to. I would recommend that you read Dr. Bernstein's book, Dr Bernstein's Diabetes Solution and keep the principles he describes in mind, though you must remember that with a child it is safer to run higher than normal blood sugars to avoid hypos, so safe blood sugar targets for your son would be much higher than those Dr. Bernstein describes for adults. Even so, he explains many other important issues relative to Type 1 that you would benefit from learning.

Ren said...

Hi Jenny,

I have test result of :
C-peptide : 2.05 (1.1 - 4.4 ng/ml)
A1c : 9.0% (4.8 - 5.9)
Insulin : 5.74 (2.6 - 24.9)
Fasting Glucose : 172 (<100)

ON MAY 3rd 2012

and then I restest ON JUNE 9th 2012 :

C-peptide : 0.43 (1.1 - 4.4 ng/ml)
Insulin : 0.690 (2.6 - 24.9)
Fasting Glucose : 343 (<100)

Is it mean that I have type 2 first then turn to type 1?

Thanks for your reply..

Jenny said...


That is a possibility, which you doctor should be checking out by giving you tests for the antibodies that would be present if you were experiencing an autoimmune attack on your pancreas. However, one test is never enough to make an absolute diagnosis, especially when it is different from an earlier test.

But that is a possibility and with blood sugars that high you should be put on insulin immediately to avoid developing diabetic ketoacidosis, which is a dangerous condition that happens when blood sugars are very high.

You doctor should be in touch with you about this soon. If not, call. If it is Type 1 it has to be treated.

NeedANap2 said...

I would appreciate your advice. Would taking metformin change my c-peptide level? I've been on metformin 500 mg twice a day for a month. I thought I would receive c-peptide results from a TrialNet study but not sure if they will give me those results so I'm considering having my dr order a c-peptide test (we have poorly paying ins so I may have to pay it all myself).
(Background - my daughter has type 1 so we went through TrialNet testing. We have 4 children. I had 3 autoantibodies present - GAD #152, ICA #10, and ZNT8 #.24 and at 2nd testing A1C #7.7% (the number following the # was my number). My blood sugar was running from 80-380 so I saw an endo. He thinks type 2 (there is a family history of that and I had gestational diabetes). My daughter's endo thinks type 1. I feel caught in the middle, reading about LADA I'm concerned that I need to start insulin. My dr was willing to wait for the TrialNet test results, I went to the 2nd phase of testing OGTT. I'm slightly overweight, he said I could lose 10 lbs, but only 36 years old.)

Jenny said...


Metformin wouldn't change C-peptide results. Type 2s typically have robust or even high C-peptides. LADA or Type 1 has very very low C-peptides. Metformin can't stimulate insulin release, it just makes existing insulin more effective by making the muscles take up glucose better and keeping the liver from dumping glucose when blood sugar is rising.

10 lbs overweight is typical of many people with completely normal blood sugars and doesn't in any way point to Type 2. When Type 2s are overweight it is often 50-100 lbs extra.
Try nagging the people at Trial net to see if they'll give you the results. Sometimes you have to be a bit annoying with these people.

Did the metformin make a significant difference in your blood sugar? If not, why not ask your daughter's endo for a referral to someone who would be aggressive in helping you sort this our (or ask him if he can help you explaining the financial situation.) There are a lot of very mediocre people practicing endocrinology out there so you really need to get a referral from someone who can sort out the good from the bad, if possible.

Unknown said...

Thank you for your blog. It has been very helpful.I have been having hypoglycemic events daily for the last 2-3 weeks. Most results are 60-75 with a home glucometer. One results was 40. My HGBA1C was 5.4. Fasting gluose 106 and fasting cpeptide 3.72. Any thoughts on what is going on with me. My endo appt is not for another month and I am extremely anxious

Unknown said...

I have also already starting adding protein to every meal and eating every 2-3 hours without much success.

Jenny said...


Call your Endo and report this problem now, especially if you are taking any diabetes drugs.

Other drugs can sometimes cause hypos too, like the antibiotic Septra/Bactrim (Trimethoprim and Sulfamethoxazole).

If you aren't taking anything, try cutting back on the carbohydrates in your meals, since it is possible you are having reactive lows caused by brief blood sugar highs after eating that result in overproduction of insulin. Eat mostly fat and protein in your meals for a few days and see if that helps. If it does, then the explanation probably is the reactive low.

But if you are taking a drug that stimulate insulin production (or injecting insulin) DON'T cut carbs further.

Jenny said...


Call your Endo and report this problem now, especially if you are taking any diabetes drugs.

Other drugs can sometimes cause hypos too, like the antibiotic Septra/Bactrim (Trimethoprim and Sulfamethoxazole).

If you aren't taking anything, try cutting back on the carbohydrates in your meals, since it is possible you are having reactive lows caused by brief blood sugar highs after eating that result in overproduction of insulin. Eat mostly fat and protein in your meals for a few days and see if that helps. If it does, then the explanation probably is the reactive low.

But if you are taking a drug that stimulate insulin production (or injecting insulin) DON'T cut carbs further.

Jenny said...


The solution isn't adding protein. It's reducing carbohydrate. It is carbs and carbs alone that cause blood sugar to rise, and that rise is what stimulate the insulin secretion.

Adding protein to a high carb meal won't help.

Unknown said...

Thank you. I have consulted my primary doc - who wants me to see endo. I have tried an atkins-like diet before and although I don't like it, I hate feely shaky and out of sorts more. I am not on any diabetes drugs. I am not diabetic. I did have a 6.1 HGB A1C five years ago but I lost about 20lbs (which i have now gained back) and my HGB A1C has been fine ever since. I do have Hashimotos and am on Synthriod. If I was having reactive hypoglycemia would I be having it after every high carb or sugar intake? My lows are not always after eating sometimes they have been 4 hours after eating. The 40 was four hours after eating a low carb lunch. Thank you for your blog it has been very helpful and thank you for your quick response.

Unknown said...

Thanks. I have tried an Atkins-like diet in the past and even though I don't like it I hate feeling shaky and out of sorts more. I am not on any diabeteic meds, I had a HGB A1C 6.1 five years ago but I lost about 20 lbs (which I have now gained back) and my level has been fine ever since. I do have Hashimotos and am taking Synthriod but that is all the meds I take. I did see my primary doc who wants me to see endo. Would I be having lows glucose with every high carb intake if it was reactive hypoglycemia? My low of 40 was four hours after a low carb lunch. I am still waiting on my insulin level and beta hydroxyl butarate. Thank you for your blog it has been very helpful and thank you for your quick response!

Jenny said...


Your body secretes an amount of insulin for your current meal based on what it needed for a previous meal, so if you suddenly cut carbs you will get a very big insulin secretion that will drive you low.

If you try cutting back on carbs gradually, one meal at a time, you should give your body a chance to adapt to the change. You may nt need to eat a strict low carb diet to control the problem. You just have to cut the carbs down to a level where they don't trigger that over enthusiastic insulin surge.

But what starts the cycle of reactive lows is getting brief high blood sugar spikes that trigger the secretion of more insulin than is needed.

Unknown said...

Thank you again. If that is the case when would be a good time after a meal to test so that I can tell if my blood sugar is in fact spiking?

Jenny said...


It's hard to know if you can catch the spike because if you are secreting enough insulin to cause a low, it may be very fleeting. Since it could happen any time between 15 minutes and an hour after eating and could last only a minute or two, it could be tough to catch.

If you have strips, you can try checking at 15, 25, 35, and 45 minutes and see if you see anything.

Unknown said...

Thanks Jenny. I will try.

Unknown said...

I believe reactive hypoglycemia can be a symptom of Hashi's

NeedANap2 said...

Thanks for your feedback. Yes, the metformin is helping to bring my
blood sugar into the ranges the dr wants 70-140. But sometimes I'm
lower and sometimes higher, and personally I'd like a range of 70-120
if possible.

TrialNet c-peptide results (this was May and it was a 2-hour glucose
tolerance test)
type time 0 30 min 2 hr
glucose 135 374 388
insulin <0.5 10.2 18
c-peptide 1.46 4.56 5.4

July (after starting metformin in June)
blood sugar 101
c-peptide 2.1 [range 1.1-4.4]

blood sugar 101
c-peptide 2.0 [range 1.1-4.4]

I see the dr in Sep. He's on vacation so I don't know his "opinion"
of the Aug labs. I'm still waiting on the May autoantibodies from

I'm still thinking LADA.

Unknown said...

I am a recently diagnosed (a month and a half ago) diabetic. They cannot figure out which I exactly am, but doctors are leaning torwards 1.5 (LADA).

I am 29 YO, very active, no health problems until now.

My C-Peptide results were 404 (reference range 298-2350, units: pmol/L)

My glucose fasting was 7.1 (reference range 3.8-6 mmol/L)

My journey began getting really high numbers (20's and a few 30's mmol/L and then I had a series of lows for weeks on end).

I'm just wondering if you can help me understand my C-Peptide results and what they will mean in terms of whether I'm T1, 1.5, possibly 2 (although docs say I don't fit the profile).

Unknown said...

I am a recently diagnosed (a month and a half ago) diabetic. They cannot figure out which I exactly am, but doctors are leaning torwards 1.5 (LADA).

I am 29 YO, very active, no health problems until now.

My C-Peptide results were 404 (reference range 298-2350, units: pmol/L)

My glucose fasting was 7.1 (reference range 3.8-6 mmol/L)

My journey began getting really high numbers (20's and a few 30's mmol/L and then I had a series of lows for weeks on end).

I'm just wondering if you can help me understand my C-Peptide results and what they will mean in terms of whether I'm T1, 1.5, possibly 2 (although docs say I don't fit the profile).

Carolyn King said...

I have hashimoto's thyroditis (taking Synthroid)and my endo sent me for more lab work to check for diabetes. My fasting glucose was 89 (range 65-99), Insulin, serum was <2 (range <17) and c peptide was <0.10 ( range 0.80-3.10).

The c-peptide was obviously out of range but I am wondering if it falls in the very low levels you are referring to.

I see my endo in two weeks but wanted to see if this was a red flag. Thanks for any insight you can provide!

Jenny said...

The C-peptide is low, but since your blood sugar at the time was well within the truly normal range it isn't likely to point to a problem.

When people have blood sugars 110 mg/dl or higher then it becomes more of an issue because they should be secreting insulin but aren't. In your case, with the normal blood sugar at the time of the test more insulin secretion could lead to lows.

Jenny said...


It's tough to know just from the C-peptide result. It would definitely suggest that you are insulin sensitive, whatever the origin. But if you are early in the LADA process you might still be making some insulin. The antibody tests that they give for LADA would be helpful in confirming a diagnosis.

But whatever the diagnosis, the focus should be on keeping the blood sugars normal. A LADA diagnoses makes doctors more prone to give you the kind of basal/bolus insulin regimen that makes normal blood sugars more attainable. With Type 2s, doctors often settle for really poor control and warn people away from insulin saying it will make them fat--which it won't do if prescribed properly, but most family doctors don't understand how to adjust insulin doses.

Anonymous said...

Hi Jenny,

I'm hoping you can help me interpret my recent lab results. I have just moved to a new state, and my new endo is questioning my type 1 diagnosis. He ordered a non-fasting c-peptide test. My result was 2.15 with a "cpep 2 hour spec of 2.1-6.6". My glucose level at the time was 176. He did not order an A1C test. (I had eaten lunch an hour prior to having my blood drawn.)

When I asked my new endo for the test results, I was told everything is normal, and not to change my regime. (I am a type 1 using insulin pump and CGM therapy. My A1C is normally between 6.2 and 6.5.) I take great pride in controlling my diabetes as well as I do.

Because my new endo won't give me any more information about these test results, I seek your opinion. If I am reading these results correctly, they indicate that I produce very little amounts of insulin on my own. Would you agree with this analysis?

Thank you for your insight and very informative site.


Jenny said...


It looks like your c-peptide came in at the bottom of the normal range. This is good news, not bad. It may point to your having one of the genetic forms of diabetes (details HERE). These cause the beta cell to be unable to secrete insulin due to a a broken gene but there are drugs that can make the beta cell secrete even with this flaw.

Several forms of MODY are often misdiagnosed as Type 1 when they are severe.

If you have that kind of diabetes you may be able to control your blood sugars with the oral drug Prandin rather than insulin. (There are other drugs that work too, sulfonylureas, but all of them have been found to raise the risk of developing heart disease.) If your doctor wants you to try one of them, demand Prandin, as it is the only safe one that works with MODY.

Unknown said...

You are entitled to your test results.

Lori said...

I recently had blood work done and one of the tests was c peptides and insulin.

My C-PEPTIDE 4.71 ng/ML and my insulin was 14 uIU/mL. Is this a sign of Type 2 or insulin resistance? Should I be concerned?

Jenny said...


As the text of this post explains, the C-peptide value only means that you are making C-peptide. You can't really determine insulin resistance from a fasting test since it shows most clearly when the body is attempting to clear glucose after eating. Calculations done on fasting values can provide very wrong estimates of insulin resistance. The only accurate way to measure it is to look at what happens to both insulin and glucose after consuming glucose.

Danae said...

Hi Jenny; Thank you for responding to a quite old blog post! And thank you for your clear, and very useful explanation about the limits of this lab test. I can see that it's not appropriate for my situation.

But, I still have questions! I am a thin, early type 2, age 59, and I suspect that my problem lies more with insulin-insufficiency, rather than with insulin-resistance. I'm looking for lab tests that might shed a little more light on that. Would a 2-hour OGTT with insulin measurements be useful for discriminating between the two? I'm apprehensive about having to carb-up for that, but I'd do it if it were worth it. Do you have any other testing suggestions? A GAD antibody test was negative.

I've been getting decent control the last couple of years with a low-carb diet and exercise, but my HbA1c recently slid from 5.6 to 5.9, so I suspect that I will soon need something more (as did my thin, active, type 2 father). I don't particularly want to start with metformin if insulin resistance isn't my problem. My BMI is 20, I don't have the markers for metabolic syndrome, and my hs-CRP is very low.

BTW, your "Blood Sugar 101" book has been hugely helpful for me, and I gave a copy to my doctor.

Jenny said...


It's very possible that insulin insufficiency is to blame. But the problem with any testing is that it may not affect how doctors treat you. The only way to ramp up your treatment or get a real diagnosis of one of the oddball forms of diabetes is to run up the kind of numbers they consider diabetic--which means horrifyingly high to anyone who follows this blog and the research.

So if you have insurance that will pay for it, the GTT would make it clear if you were overproducing insulin or low on it. But I'm not sure it would be worth paying for the test if you had to cover it yourself, because I don't know that it would change how your doctor would treat you.

If your A1c continues climbing that would be likely to catch their attention. Sometimes the GAD antibodies take a while to show up, so a repeat test if you can see your control deteriorating might be in order.

If you have one of the genetic forms of diabetes that don't involve an autoimmune attack, your options are to have the genetic tests done (expensive and not always conclusive), or to try Prandin once your blood sugars have gotten uglier. A strong response might point to having one of the commoner forms.

MODY shouldn't progress if you are controlling your blood sugar, though.

So while the GTT would tell you if you were insulin sensitive, it wouldn't necessarily point to treatment. You can't use insulin until you are going up into the high 200s after eating whatever amount of carbs you'd like to be able to eat. It's too dangerous to use it with near normal blood sugars.

Unknown said...

Hi Jenny,
I wrote to you back in august about repeated hypglcemic events. Well the events have calmed down somewhat and I finally got my endo appt. Rather than do the 72 fast in a hospital my dr said since i am a nurse at busy peds practice, i could fast until my glucose was at or below 65 and draw labs at work. Well i waited all day until 4pm and finally my glucose dropped to 61 using my home blood glucose meter, I had my blood drawn but it was a hard stick. My results were
Glucose 71
Insulin 4
C Peptide 2.66
Betahydroxybutyrate 0.29
Cortisol 5
My 24 hour urine collection was normal. No insulin antibody tests were ordered. I am not diabetic and am not on any diabetic meds.
My dr office left message for me today and said my dx was reactive hypoglycemia and to see a nutrtionist.
I have been gaining weight with no chnage in diet, I am up 10-15 lbs in the last two months and I have pain in my side - middle right. Do you agree with this? Any thougths would be greatly appreciated. All the research I have done states that these tests are pretty useless unless glucose is <55 at the time of testing?

Jenny said...


A glucose of 71 is actually normal. the normal range extends to 70. Home meters can read low. Mine read 9 mg/dl low when I took it to the lab.

Your fasting insulin is perhaps a tiny bit high, hence the hypoglycemia diagnosis, but by no means significantly high. What was the lab normal range for fasting insulin?

With the information you've provided I'm not sure how your blood sugar, which is basically normal, would be related to your other issues.

The usual advice for dealing with reactive hypos is to eat smaller meals high in protein (and low in carbs) to avoid the blood sugar spikes that cause the reactive lows. Basically it is spikes in blood sugar that cause reactive lows. But if you were FASTING, this wasn't a reactive low, and besides that, 71 mg/dl isn't a low! It sounds like your doctor is just handing you off because he doesn't see anything to treat.

Unknown said...

The lab lists <17 as normal but I am not sure if these are fasting levels or not. the only lab marked abnormal is the betahydroxybutyrate normal levels listed as 0.28 or less.

Unknown said...

I was fasting from 1000pm the night before until 400pm the next day as I was told the test could not be performed unless glucose was at 65 or less. Basically i was fasting to elicit a hypo event.

Jenny said...

Well, those are very normal numbers for fasting, then. But that's an odd way to test or diagnose.

Unknown said...

She was testing for an insulinoma as probable cause of the hypos

gaffgolf said...

Dear Jenny,

64 year old male with 10+year type2 on meds with recent jump in A1C (7-11.9)suggesting the need to start insulin. Dr. has approved a C-Peptide. Should I request a non-fasting test and, if so, what do you recommend I eat and how long before the actual test in order to get the most accurate reading of my insulin production? Anything else you can recommend to prepare for the test? Thank-you for a prompt response.

Jenny said...


Your doctor should have specified if it is to be a fasting or non-fasting test. If you aren't sure, call and find out.

The C-peptide (as the post above makes clear) gives only a minimal amount of information about your insulin production--if it is extremely low, it will tell the doctor that your pancreas isn't producing insulin. If it isn't extremely low, it only tells him that you are type 2 and possibly that you are insulin resistant.

Unless it is almost nonexistant it won't be helpful in dosing insulin. And with a blood sugar that high you should be put on an insulin regimen that uses a basal insulin to control fasting and a fast acting insulin at meals, dosed to match the carbohydrate content of the meal. This may require visiting an endocrinologist. Family doctors are often very bad at prescribing insulin properly.

gaffgolf said...

Dear Jenny,

Thank-you for a prompt reply. I had read most of the blog comments before seeing my doctor yesterday.

The comments seem to suggest that by the fasting test, the pancreas isn't truly tested because of no insulin output since no meal intake. I understand that test results (ranges) are different for fasting(lower) and non-fasting(higher) but do you have a preference and if it is for non-fasting, what level of glucose and how long before the test should I consume it??

BTW, in our discussion the Dr. wants to start me on a 70-30 insulin to be injected twice a day before meals. Initial dosage to be increased as necessary to lower BS. Continue Metformin @2000 a day and drop glipazide @5mg twice a day before meals.

Jenny said...

70/30 insulin is a mix of fast acting and basal insulin. It makes it extremely hard to get anything near normal blood sugars. If you are willing to study, you can do a lot better with separate basal and mealtime (fast acting) shots. To learn how to use insulin read John Walsh's book, Using Insulin. The book, Dr. Bernstein's Diabetes Solution also has a lot of useful information about how to use insulin. Between the two you will get enough understanding of insulin to ask your doctor for a better insulin regimen, or to go out and find a new doctor who is willing to prescribe a more effective insulin regimen.

As far as the C-peptide test goes, I believe most labs just provide a fasting range and if you aren't fasting the number you get can't be interpreted. You would have to talk to your doctor and he'd have to check with the lab to find out if they even do a non-fasting C-peptide. In any event, the number you get from any C-peptide test is NOT ACCURATE and as the article above points out (and everyone ignores) do the same test on the same sample at the same lab twice, and you get two different values!

It's more important at this time to put your energy into getting a modern insulin regimen. Once you are using fast acting insulin (dosed to the amount of carb in your food) you will learn exactly how insulin resistant you are. But with 70/30 you can't dose the insulin to match your carb intake and will hypo if you try to adjust the insulin dose to your meals.

This is more than I can explain in a single post, but I urge you to read up on the topic if you are serious about avoiding diabetic complications.

gaffgolf said...

Thanks Jenny-I will be reading the books you suggest!
BTW, had 2 C-Peptide tests (at different labs) and results were 2/3rds into the range for each lab-i.e. tested 2.5 in a range of .5-3.5. Doctor termed insulin being produced as "faulty and non-functional" and I have set appt. for injection training.

Perhaps you can help me in understanding why my A1C jumped from 7 to 11.9 over a 5 month period when my meds, diet and exercise were the same as the prior periods. Why did this skyrocket when it was always under 7 for 10+years? I can only think something failed in my insulin production process? Have my beta cells failed??

Jenny said...


The C-peptide is usually tested fasting. But fasting insulin secretion is a separate system from meal-time insulin secretion, so most likely your beta cells have stopped being able to secrete insulin in response to rising blood sugar at meals. This is a common problem that occurs with beta cells.

Meal-time insulin would be the best solution. If cutting back on carbs doesn't lower your post- meal blood sugars (as in the strategy described HERE you need to use fast acting insulin (novolog or apidra, ideally) carefully matched to your carbohydrate intake. A basal insulin (lantus or levemir) won't likely be enough to bring your blood sugars down to the safe zone as they mostly correct fasting secretion.

Adam Becker Sr said...

If C-peptide has some useful function, then is it missed?

I'm DMT2, currently low carbing at < 20 g / d. (Aside: Working great! Easiest 12 lbs I ever lost and my blood glucose numbers are the best since diagnosis!)

But since I'm living on ketones, then I need hardly any insulin. So I guess I make hardly any insulin, right? Which should mean that I'm hardly making any C-peptide any more. Is that a good thing? Did I need that C-peptide for something?

Jenny said...


You are still making insulin because without insulin you couldn't metabolize the glucose that your liver manufactures from the protein you eat and is used to run the neurons in your brain that can not burn any other fuel.

That's why people with Type 1 on Bernstein diets (and Dr. Bernstein himself) must still inject insulin several times a day and why before the discovery of insulin people with Type 1 on "starvation" low carb diets eventually died.

You aren't making as much insulin, but in the fasting state your C-peptide can be interpreted using the vague diagnostic ranges.

But no one should interpret the C-peptide as showing much more than that they secrete insulin in normal, supranormal, or subnormal amounts. Beyond that, it isn't possible to tell from this test.

Adam Becker Sr said...

Jenny writes: "You are still making insulin because without insulin you couldn't metabolize the glucose that your liver manufactures from the protein you eat and is used to run the neurons in your brain that can not burn any other fuel. "

Are you sure that's quire right?

(1) Insulin is necessary for glucose to enter muscle, but not to enter neurons, yes? (A type I with no insulin will stay conscious as long as they keep eating dextrose, IIRR.) A quote: "It should be noted here that there are some tissues that do not require insulin for efficient uptake of glucose: important examples are brain and the liver. This is because these cells don't use GLUT4 for importing glucose, but rather, another transporter that is not insulin-dependent."

(2) By the time I'm fully ketoadapted, my brain is mostly (80%) running on ketones. (At least, according to Phinney & Volek in "Art and Science of Low-Carbohydrate Living")

Jenny said...


You may be right about the brain, though I'm not 100% sure that it functions well over time without glucose. A Type 1 will stay conscious with glucose if they are hypoing, but that usually occurs because they took too much insulin.

Type 1s will die without insulin even if eating very low carb diets or for that matter, no carb diets. Children with Type 1 typically died within a year or two eating extremely low carb diets, and like I say, even Dr. Bernstein who has been eating a ketogenic diet for decades injects insulin several times a day. About 10 units or so, if I recall correctly.

Adam Becker Sr said...

There's an account in one of the two Phinney & Volek Art and Science books (I read them back to back, so they blend together...)

Some time back (i.e. before modern patient safety review boards) Doctors took obese diabetics who'd been hospitalized. They put them for several weeks on a very-low-carb diet. When they were fully keto-adapted, the doctors gradually infused insulin until the patients bG went down to 30 mg/dL (!) The patients were alert and reported no discomfort.

Jenny said...


Having experienced having my blood sugar drop down into the 40s myself without noticing it, (not on purpose and when not in a ketogenic state), I'm not sure this study means much.

When people lose hypo awareness (which is what happened to me during my last weeks on Prandin) they will feel fine until they suddenly pass out, perhaps a bit lower.

Plus, since this study is old, the blood glucose monitoring may not have been all that accurate, so that reported 30 might be higher nowadays. For example, all the meter readings in the 90s in the 1990s would be in the 1-110 range now due to changes in how meters are calibrated.

The research I've reviewed suggests that your brain still needs 40 g of glucose a day to function. But most people eating ketogenic diets are getting that glucose from gluconeogenesis, which means that their liver transforms about 70 g of dietary protein into glucose every day. If extra dietary protein isn't available your liver will cannibalize muscle.

It is extremely dangerous for Type 1s to attempt to control their blood sugar with only a ketogenic diet. I doubt that is what Volek & Phinney are suggesting is possible, because it isn't, and to suggest it is possible for people with Type 1 is to ask them to risk their lives.

That said, I have heard some horrifying stories from people with what turned out to be Type 1 diabetes who were treated by doctors who have a high profile in the Low Carb fanatic community who completely missed the diagnosis and insisted their skyrocketing blood sugars on the low carb diet were due to noncompliance. Sadly, very few doctors who were not trained specifically in endocrinology know squat about diabetes. (The Atkins diabetes book is full of statements that simply wrong.)

Unknown said...

I have PCOS, I get severe hypo episodes especially at night in sleep etc... My blood work is as follows:

fasting blood glucose-100

hemoglobin A1C-5.7


Does this mean I am insulin resistant? Or does this mean insulinoma etc? -Heather

Jenny said...

Heather, The whole point of this original post is that the C-peptide test is so vague that doesn't tell you anything more than that you are producing insulin.

The test result should have been accompanied by a reference range which would define normal levels. If your test value is way over the top of the reference range (i.e. way over normal) you would know you had high levels of insulin. There is no way of determining if high levels would be from PCOS or from some other cause simply by looking at this set of blood tests. PCOS used to be diagnosed on ultrasound when women were found to have ovarian cysts. Hirsutism and high androgens were another important finding. Nowadays PCOS seems to be getting applied to many people without the clear cut signs. I don't know if this makes it more likely to be misdiagnosed or not. Insulin resistance on its own may be genetic in origin as many people seem to be born with it, especially people with strong family histories of Type 2 diabetes.

In any event, to avoid the hypos try cutting way back on the carbohydrates you eat, especially for dinner. The less carbohydrate you eat, the less your blood sugar will rise and the less it will provoke the secretion of the large burst of insulin that causes the hypos hours after eating.

Unknown said...


First off I want tothank you for your contribution to this website and helping people.

if any of this matters I'm 32 years old. I have an autoimmune disorder and no immune system and I have an abnormally high T cell count. I am on 18 different medications that go through both the liver and kidneys. Including a couple of nasty biologic medications. I have never had problems in the past with blood sugars, C peptide, or insulin levels or anything having to do with the endocrine system.

my Rheumatologist sent me out for fasting blood work this past Friday. The lab values are as following:

Insulin 57.6 range 2.6-24.9
C peptide 7.8 range 1.1-4.4
BGL 98

my Rheumatologist says that I have a metabolic syndrome and is referring me to the Joslin center.

so I have some questions the first one is what defines metabolic syndrome?

if the C peptide levels are supposed to be five times higher than the insulin does that mean I could have problems with my kidneys?

I am sure at the center they will want to run a a1c test. the question I have about that is regardless of what that test result shows, does that mean I need to be treated by metformin or any of the other medications.if so why would I want to do that if my blood glucose levels are normal.

Thank you,

Jenny said...


Metabolic syndrome is one of those garbage can invented syndromes used to cover a number of not always related things like high blood pressure, abdominal obesity, and insulin resistance. Since these can all come from unrelated causes, it doesn't really mean that much, though when all the symptoms are present, it can increase the risk of developing heart disease as you age.

However, your insulin/c-peptide results suggest only that you are insulin resistant--i.e. you are using more insulin than normal to keep your blood sugars in line, but you are keeping them in line. You may also develop high blood pressure because high amounts of circulating insulin can push up blood pressure, mostly because of how insulin affects sodium levels.

Given the amount and types of medication you are probably taking with an immune condition, this elevation of your insulin resistance is almost certainly due to the drugs. Cortisone, for example, will do this. So do the life-saving HIIV drugs.

Metformin is not safe to take with drugs that affect how the kidney eliminates other drugs, and it may also conflict with how drugs are affecting your liver. You need to see someone knowledgeable about your specific condition, not some local endocrinologist (some of whom, sadly, were trained years ago, don't keep up, and can be very ignorant about situations like yours.) So Joslin is probably a good place to go, as it has some very skilled endocrinologists. But even so, make sure that whoever you see is familiar with your other condition and the drugs you take. Don't be afraid to ask if they have treated many people with your condition.

I have a fairly rare inherited condition affecting my liver and cannot tell you how many times I have been prescribed drugs that would be toxic to me (and in one case, were.) So I've learned not to trust any expert, and if a drug is prescribed, I always read the official Prescribing Information intended for physicians to make sure that it doesn't flag my issue as one doctors are supposed to pay attention to. In some cases I have been prescribed drugs that have black box warnings for my condition even after explaining it to the prescribing specialist (I.e. the drug could be fatal to me!)

The most important measure of blood sugar isn't the fasting measurement but what happens 1 and 2 hours after you eat. If those readings are under 140 m/gdl (which you can check with a blood sugar meter) or at worst under 160 (some meters read high) then you don't have much to worry about. If your readings are high after eating and remain high for several hours--for example over 200 mg/dl, then you are risking damage to your nerves, kidneys and other organs, and do need some treatment.

The doctors at Joslin should be able to help you sort this out.

Unknown said...

Hi Jenny,

1st of all I would like to thank your for your contributions and helpfulness.

Just a little history: 32 years old chronic infections and hospitalizations. Auto-immune disorder, No immune system (WBC hover 0.25-1 even when sick), T cell count through the roof..... etc.... pretty much any immune thing you can think of I guess. I take 18 different meds going through both the liver and kidneys, including a couple of biologics that are nasty as hell. (Anything else you need to know let me know)

So I fired my old Rheumatologist because he was a scum bag and the new one I went to was this past Friday. He ordered fasting C-peptide and BGL.... Also a slew of other things like antibody studies, immune response studies, prophyria, and a lot more but they have not come back yet.

Insulin is 57.6 range is 2.6-24.9
C-peptide is 7.8 range is 1.1-4.4 (I know this does not mean anything by itself because it isn't low)
BGL 96
This was actually a 48 hour fast
My appetite is crap and I am lucky to eat one meal a day.

He said that I have Metabolic Syndrome (Which after looking it up I do not agree) and that I have to go see an Endocrine doc at the Joslin Center and most likely they will run a a1c.

So I guess my questions are....

If from what this post says in the beginning since my C-peptide levels are not 5 times higher then the Insulin levels is could there be a problem with my kidneys?

Even if the Endocrine doc runs all the tests in the world do I have to add another stupid med(s) to my list when obviously my body does fine with Sugar levels... or and PS fasting and non-fasting I check it at home sometimes it is always normal. Hospitalizations they run Endocrine studies and they are always fine.

If further studies show that my Sugar is high and they want to put me on something with a needle I do not know what I would do. I have a list of things that I absolutely cannot do especially needle sticks.... Hell I probably shouldn't even do finger prics to test. My last hospitalization was secondary to a staff infection in my blood due to a blood work stick. Any suggestions there?

I think that is all I would like to ask for now.

Thank you,

Unknown said...

I did not realize the lag time before it actually posts to the blog but the Second one I sent you there is an additional question plus I think I worded one differently.

I would also like to note that I already have HTN and Tachycardia that is being treated with a Beta Blocker. That was only recently diagnosed. So if this is because of High Insulin levels then treating that could treat the HTN and Tachy rythm, right?


Jenny said...

As this blog post states very clearly, the C-peptide is useless for telling you anything more than that a) you are making insulin, b) you are not making insulin, or c) you are making a lot of insulin. There is no ratio to the measured insulin that means anything, and measured insulin can be a highly erratic test. Don't read anything into it.

If you can't get your blood tested because of the fear of infection it would be extremely hard for any doctor to evaluate your blood sugar status. Given that your fasting blood sugar was within the normal range, this isn't any kind of emergency, and it sounds like you have enough to deal with already. Do you have a primary care doctor you could talk this over with? Your situation is complex enough that you do need feedback from someone with medical knowledge who is familiar with your history in the way that no one posting online could be.

Jenny said...

Beta blockers will also increase your insulin resistance. But if you need it you need it. Never stop taking one of those without medical supervision as stopping one can cause a heart attack if done too quickly.

Shira said...

hi! i was diagnosed in January as type 2. I am 26. Recently, my endocrinologist took more blood work to test my c peptide and GAD levels. My fructosamine was 366 ( range was 190-270). My c peptide was .74 (range was .80-3.1) and gad was >30 (range <=1.0). I am on novolog and lantus.


Jenny said...


It is very likely that you have LADA, the slow onset form of autoimmune diabetes, which you can read about HERE.

LADA is becoming more and more common though no one is certain exactly why. Functionally, it is the same as Type 1 diabetes.

Hopefully, your doctor will explain this to you at your next appointment. If not, you should seek out an endocrinologist who is better at communicating with patients, as it will take a lot of communication to learn the best doses for you.

I would suggest you read John Walsh's book, Using Insulin, to get a better idea of how insulin should be dosed for Type 1. The book, Dr. Bernstein's Diabetes Solution will also teach you a great deal about controlling blood sugar, even if you don't eat the very stringent diet that Dr. Benrstein recommends.

Cutting back on your carbs to some extent, so that you can lower your insulin requirements to a level that makes it less likely you will have dangerous low blood sugar attacks (hypos) will probably be useful.

There are several forums on the web where people with LADA (sometimes called Type 1.5 Diabetes) discuss issues. You can learn from the people there, too.

Anonymous said...

Angela here: My doctor said on Jun 13 that the diabetes with I'm affected IS LADA. Which carbs should me and Sammie restrict? Because cutting back on carbs is more complicated than one thinks. Furthermore, we wanna lower our insulin requirement so that the risks of hypoglycemia are much less. The last thing I wanna do - suffer my father's fate (he was diagnosed with T2D in November 1992 and had ketoacidosis eight times; he passed away in August 2008 after a heart attack at age sixty-four). He did not know LADA really existed. American Diabetes Association does not really have too much on Latent Autoimmune Diabetes of Adults. They do, however, say, Diabetic Ketoacidosis can sometimes occur with Type 2 Diabetes, which me and Samantha find very questionable.

Jenny said...


All carbs raise blood sugar, the only difference is how quickly they digest. When you aren't producing insulin the so-called glycemic index doesn't apply. It describes what happens with fast and slow carbs in people who have intact second phase insulin response.

I would suggest that you use the technique described HERE to find out what carbs work best for you. Since you are using insulin, you must make any changes to your carb intake cautiously, since cutting too fast may cause hypos.

This comment section isn't the place to discuss the treatment of LADA. I would suggest you find some diabetes forums where there are active discussions going on. Many have a "Type 1.5" section where LADA is discussed.

natureboy said...

I was diagnosed type 2 in 2007. My recent A1c was 8.0. My c-peptide then was 0.78. Could my metformin be lowering my c-peptide? Would decreasing metformin likely raise c-peptide? What else would raise c-peptide?

Jenny said...


What lowers C-peptide is not making very much insulin. Metformin wouldn't do this. You might talk to your doctor about adding insulin to your daily regimen. If your C-peptide keeps dropping you may have to. The good news is that used properly it will greatly improve your blood sugars.

Unknown said...

my 16 month old as hospitalized with a blood sugar level of 30 in March 2013 and then she went back to the hospital with a blood sugar level of 60 in August. She had blood work done last week and her c-peptide came back .21 and is should be .81-3.10, her glucose was 75 between 65-99, however her Alk Phos was 5199 and its supposed to be between 108-317. Yes 5199.
Are you familiar with this? Can you explain what 'could' be going on?
Thank you

Jenny said...


I am so sorry your toddler is undergoing such a difficult time. Unfortunately, I don't know why her liver enzymes were so high, but the doctor who ordered this test should be explaining this result to you. If you haven't heard from the doctor you must call their office or clinic and demand to know what these test results mean and what treatment your daughter needs.

Unknown said...

Thank you so much Jenny.
I called and the doctor said he would rather discuss it at our appointment which is Dec 13th. I am praying everything is ok.

Do you know the causes of her C-peptide being so low. it was .21.

Thanks again,

Jenny said...

I would hope that if the doctor doesn't think your child needs to start treatment right now with something, it can't be too serious. But it is really cruel to leave a parent in suspense for so long!

With a normal fasting blood sugar, the low C-peptide may not mean anything. C-peptide gives a very rough approximation of insulin. Low insulin levels are only of concern when people have high blood sugars.

There is a condition that happens in young children where their Alkaline Phosphatase rises to great heights, but in a few months it clears up on its own. It doesn't appear to point to a disease. Let's hope that is what your child has.

Unknown said...

hi got my fasting c-peptide result.. my result is 1.80 ng/mL and the range is 0.78 - 5.19 ng/mL..

and my FBS is conventional units 105.60 reference range 70.00 - 100.00mg/dl

it means its a normal result or i have enough insulin?

Jenny said...

That looks like a normal range for for making insulin and a very slightly high fasting blood sugar.

Unknown said...

hi jenny
you mean my insulin is good?

how about my FBS? im a prediabetic or diabetic?

thanks in advance :)

Jenny said...

The C-peptide test shows that you were making some insulin. Since it is not a very accurate test (the whole point of this blog post) that is all you can say with certainty.

Your fasting blood sugar was slightly elevated. By definition, a fasting blood sugar has to be over 125 mg/dl to be called diabetic. Yours would be labelled "prediabetic" but it would be wrong to make any diagnosis based on a single test, and besides, fasting blood sugar is the least informative test if your interest in blood sugar is to avoid it damaging your organs.

I would suggest you read up about blood sugar levels on the main Blood Sugar site.

Your post meal blood sugars are the most important, and your goal no matter what diagnosis you are given is to keep them in the range that avoids organ damage. This post meal range, according to a lot of high quality research is under 140 mg/dl.

Unknown said...

hi jenny
my doctor told me to take this test called PPBS my resul t is 181.10 mg/dL

he told me to eat heavy meal then after two hours after meal i got this test.... PPBS


Jenny said...

Bryan, Those are pre-prandial (before a meal) and post-prandial (after meal) readings.

To better understand what they mean--and why you should be testing at home, you will have to read the detailed explanations found on the main Blood Sugar 101 web site.

At a minimum, read the pages about what is normal blood sugar, what blood sugars cause organ damage and how to lower your blood sugar.

Your pre-meal blood sugar is high enough to do some damage, so it's time to get started bringing those sugars down. Fortunately this is very possible.

Unknown said...

miss Jenny one more thing
my PPBS is high.... it means im a diabetic or pre-diabetic

thank you :)

Jenny said...

That pre-meal number is high enough to damage your eyes, kidneys and nerves, whatever the doctor calls it. Please do read the pages on the main site that explain this in detail. You need to work on lowering your blood sugar safely.

Donna said...

Hi Jenny,
I am enjoying reading this blog and all of your associated reading material. I was diagnosed last year at age 56 as a type 2 diabetic. All my life I have been (and still am) extremely fit with very low body fat (an athlete) and always eaten lean, healthy, fresh foods. My fasting sugar used to always be low (~56). My two endocrinologists are puzzled. My c-peptide levels show that I have insulin deficiency, but have no antibodies, so type 1 was ruled out. Can stress cause diabetes? I just got out of a very stressful job that I had for nearly seven years and wonder if I was damaged by it permanently. Luckily, all of the rest of my bloodwork looks fantastic--just my sugar is bad. Have you seen this before?

Jenny said...

Stress cannot cause diabetes of the type you describe, and though short term physiological stress of the kind you feel when escaping a charging lion does raise blood sugar, it doesn't raise it permanently. And more importantly, it will also raise insulin resistance. In contrast, damage to the beta cells alone usually leaves a person insulin sensitive.

Sometimes when people develop the adult form of Type 1 it takes a while for the antibodies to show up on tests. Alternatively, they may not have the more common form of antibodies (GAD antibodies) but may have another type.

Your doctor should treat you with insulin to prevent the high blood sugars you have from destroying your beta cells if something besides an autoimmune attack has taken them out. (And to avoid complications long term.)

With diabetes it is important to realize that no matter what the cause of the diabetes, what matters is keeping the blood sugars as close to normal as possible. That is because in almost every situation it is the high blood sugars, not the underlying cause, that results in diabetic complications.

Concentrate on keeping your blood sugars normal for now and over time you will probably get more signs pointing to what the origin of your diabetes might be.

But if you are concerned because you don't think you fit the profile of people who get Type 2 diabetes, since you are brainwashed by the media-promoted idea that they cause their diabetes with poor choices, it's important to know that isn't true. People with Type 2 usually have genes that predispose them to diabetes or have been harmed by toxic exposures to the many environmental poisons and pharmaceutical drugs that that cause diabetes.

Donna said...

Thanks, Jenny. I will keep focused on keeping my blood sugars down and try to save my remaining beta cells. Thanks for the great links on helping to do that.

Unknown said...


I have a CPEP result of 2:18 & Insulin Level of 43 what does this mean? I've been a T2Dm for about 4 years now, is this a good number to have?



Jenny said...


Your numbers suggest that you are making insulin in quantities typical of an insulin resistant Type 2 rather than someone who is insulin deficient.

Neeraj Sharma, Punjab, India said...

Hi Jenny..
My 10 yrs old son was diagnosed with T1 diabetes on 05-09-2013.. at that time his fasting BG is >200 and C-Peptide is <0.30
Dr. advised him advised him 24 units of Homologue insulin in a day(3 times)..
Now his insulin requirement reduced to 12-14 units in a day...Now days his BG level is near about 100mg/dl fasting and random.
and C-Peptide fasting level is 0.84..
Is it means that he is covering from this diseases..and in future he needs no insulin..?

Jenny said...


Sadly, if your son truly has Type 1 diabetes he won't recover from it. However, it is common for people with Type 1 to experience the kind of improvement your son is seeing. This is called "the honeymoon period." If you continue to keep his blood sugar under control, he may stay at this stage for a long time.

However, there is always the possibility that your son was misdiagnosed and really has Type 2 diabetes. Your doctor can check this out by giving your son a test for the antibodies associated with Type 1. If a year or so after the diagnosis he does not have these antibodies in his blood, then it would be possible he has Type 2. Type 2 doesn't go away either, but it can be controlled by eating a diet low in sugar and starches and with metformin, an oral medication.

In either case insulin seems to be keeping his blood sugars in a very good range, so you should not stop it. Many doctor allow people with Type 2 diabetes to run blood sugars high enough to damage their organs and destroy their remaining insulin-secreting cells. The only time to cut back on the insulin would be if you son started seeing values in the 70s or lower and was in danger of hypos.

Unknown said...

what are the measure parameter to differtiate in type i and type 2 diabetes

Jenny said...

The test result should be reported with a reference range. Type 1 would be indicated by a very low reading well below the bottom of the reference range. Type 2 typically will result in readings 2 or 3 times higher than the top of the reference range. But as this article points out, the test is not at all precise. Very low and very high are meaningful.

mkcarman said...

I was diagnosed as a Type 2 15 years ago. I used prandin for about three - six months and even with increasing doses, I had to go on insulin. At first the insulin was just long acting and within a couple of years I as doing MDI before meals as well. For years ago, I went on an insulin pump which has been great. I started out at 48 units a day total and now use anywhere from 30-35 units a day total.

In 2013, my prior endo did a C-peptide on me and it came back at 1.1, low end of normal. She did not run a fasting at the same time and she insisted that I leave my pump on and running at the time of the test, as usual.

Fast forward to a new endo, someone in the same group, and he believes I may have LADA based on the small amount of insulin used as well as how quickly I became insulin dependent. He wants to do another C-peptide as well as other autoimmune tests to confirm the LADA before I hit medicare age in three years. We will wait until closer to the Medicare time so that the reading will be more relevant. Next time, do I leave my pump on for the tests and, what are your overall impressions about the possibility of LADA given the low insulin needs and the quickness of becoming insulin dependent. Thanks.

Jenny said...


LADA is definitely a possibility but that C-Peptide was high for LADA. There are some other forms of diabetes that cause failure to secrete insulin, including the MODY forms. I know several people with MODY-3 who use pumps and the amount of insulin you use. Those forms don't involve autoimmune attack. (OTOH, with MODY-3 you would have been likely to have responded more strongly to Prandin.)

So to diagnose LADA you need to also test for the GAD and islet antibodies rather than just the C-peptide levels.

But what difference would it make for your treatment to have such a diagnosis? If you had one of the MODYs that respond to sulfonylureas you could switch, but most people I've talked to who have gone that way have hated the sulfs. You get much better control with a pump. If you have LADA, there's no change in the treatment.

Unknown said...

Hello..I have Mody-3 and I have been dealing with the highest doctor about it. They found out my body is rejecting all insulin and pill a1c is always at 9.5. Yet I excercise everyday eat real good and lost 232 pounds and still losing. My blood sugar never goes under 275 and when given insulin no matter how many units it goes to 400. Just Thursday they told me there is nothing they can do for me and told me how the disease will kill me and to be prepared.
Please is there anything I can do different? Please let me know!!
Princess Buffalo

Unknown said...

I don't have diabetes, my doctor said I don't, but she is referring me to an endocrinologist because my c-peptide was 7.5. normal is .8-3.9. Is that really high? Im a 22 year old female with no history of diabetes or pancreas problems and I'm thin and healthy. Should I be scared?

Jenny said...

Aneedra, Have you tried eating a very low carbohydrate diet? Where you mostly eat fat and a modest amount of protein and very little starch and sugar. That should bring your sugars down to some extent simply because those foods requires very little insulin.

Beyond that, have you been put on U500 insulin, which is a much more concentrated version which works extremely well for people who have developed antibodies to insulin which keep it from working. This treatment is appropriate for people who aren't responding to insulin.

I would also strongly suggest that you go to this page: Diabetes Genes: Contact Us and email Dr. Maggie Shepherd using the email given there. She and her associate Dr. Hattersley may have some more ideas for you.

To learn more about how to eat a very low carb diet that should keep your blood sugars low enough to sustain you while you find more helpful medical staff, you should read the book, The Diabetes Diet by Dr. Richard K. Bernstein.

I don't know what medical resources you have available, but I have heard from other people whose doctors gave up on them who did find help from doctors at Stanford Medical School, too. Don't give up! There are treatments that may help you!

Jenny said...


You shouldn't be scared. But that test result suggests that you are very insulin resistant. This could point to Polycystic Ovary Syndrome which might cause problems should you wish to become pregnant. It is treatable.