What best predicts diabetes in people who are in that middle ground of not normal but not frankly diabetic is the result seen on a blood sugar test taken one hour after a glucose challenge--i.e. after eating a significant amount of carbohydrate.
You can read this study here:
Minimal Contribution of Fasting Hyperglycemia to the Incidence of Type 2 Diabetes in Subjects With Normal 2-h Plasma Glucose. Muhammad A. Abdul-Ghani. Diabetes Care March 2010 vol. 33 no. 3 557-561. doi: 10.2337/dc09-1145
In this study the researchers looked at the records of 3,450 subjects who started out with 2-hour plasma glucose concentration <140 mg/dl.[7.7 mmol/L] These subjects were participants in the San Antonio Heart Study (SAHS) and the Botnia Study for 7–8 years.
The researchers found that while incidence of type 2 diabetes at follow-up was related to the fasting, 1-h, and 2-h plasma glucose concentrations,
... when the 1-h plasma glucose, but not 2-h plasma glucose, concentration was added to the model, FPG [fasting plasma glucose] concentration was no longer a significant predictor of type 2 diabetes in both studies (NS).I get a lot of mail from people whose home testing is showing blood sugars well over 140 mg/dl (7.7 mmol/L) but whose doctors insist they are "fine" based on their fasting glucose readings.
When subjects were matched for the level of 1-h plasma glucose concentration, the incidence of type 2 diabetes markedly increased with the increase in 1-h plasma glucose, but the increase in FPG was not associated with a significant increase in the incidence of type 2 diabetes.
If you fall into that category, and are having trouble getting your doctor to take your concerns about your blood sugar seriously, track your one hour blood sugar test results and if they are routinely over 140 mg/dl, print out this abstract and take it with you to your appointment.
You can learn how to use a blood sugar meter to test your blood here:
Am I diabetic? How to test your blood sugar to find out.
There is a less common variant of diabetes usually seen in males where the fasting blood sugar is very high but post meal blood sugar is not. If you have normal post-meal blood sugar, but see fasting blood sugars heading towards 120 mg/dl (6.7 mmol/L) you might be developing diabetes in this manner. Over time it may proceed to full fledged diabetes. Because most family doctors diagnose diabetes based on fasting tests people who develop diabetes in this pattern are more likely to have their diabetes diagnosed early.
You can read about what research has revealed about the different patterns in which diabetes develops and the likelihood of having your blood sugar dysfunction progress to diabetes HERE .
But what if your blood sugar is not going over 140 mg/dl when you eat carbohydrates? Unless your fasting blood sugar is near 120 mg/dl, you are fine. This sounds obvious, but I get a surprising amount of mail from people who have normal fasting blood sugar and normal one hour readings who are convinced there is something wrong with them. There may be, but it is usually not because they are developing diabetes.
That's because normal people's blood sugar fluctuates and may reach the upper 130s an hour after eating and then drop back to normal. The only time you might have a valid concern if your blood sugar at one hour is spiking into the 130s is if it is still in the 130s two hours after eating and even three hours after eating.
This would suggest that your body is having trouble with its second phase insulin response, which you can read about HERE. But this is rare. The most common progression to diabetes begins with one hour readings over 140 mg/dl that resolve or even produce reactive hypoglycemia. This then proceeds to readings over 140 mg/dl that stay over 140 mg/dl for another hour or two.
Though this is technically the "prediabetic range" researchers now know that the incidence of neuropathy, heart attack, and diabetic retinopathy all start to rise as one hour blood sugar goes into the range over 140 mg/dl. (More about that HERE and HERE)
If steps aren't taken to lower blood sugar when it is in the prediabetic range it may rise eventually into the official diabetic range--over 200 mg/dl. But it is very foolish to do what too many family doctors do--ignore oncoming diabetes until a person has an official diagnosis.
That's because the interventions that lower blood sugar are so much easier and more effective when you begin them when blood sugar is only modestly abnormal. When you are only seeing spikes slightly above 140 mg/dl at one hour, usually all it takes to lower blood sugar is to cut down on the amount of carbohydrate you eat at each meal.
Because blood sugars over 140 mg/dl are toxic to the beta cells that produce insulin and can, over time, kill enough of them to make you permanently diabetic, taking steps early can keep your diabetes from progressing, whatever your family history might be.
And because the most effective intervention is one that requires no prescription or help from a doctor, there is nothing to keep you from embarking on a program of healing whether or not your doctor takes your mildly abnormal blood sugars seriously.
You'll find detailed instructions for how to lower your blood sugar safely on your own here:
How to Get Your Blood Sugar Under Control