Seeing into the future: predicting the progression from prediabetes to type 2 diabetes

This study examined predictors of the progression from prediabetes to type 2 diabetes.

In prediabetes, blood glucose (sugar) levels are higher than normal, but not yet at the levels necessary to be diagnosed as type 2 diabetes. Patients with prediabetes generally present with impaired fasting glucose (inappropriate levels of glucose after a long period without eating or drinking) and impaired glucose tolerance (glucose levels are higher following eating or drinking compared to those without prediabetes). These patients are at a high risk of developing type 2 diabetes.

Because the number of people suffering from type 2 diabetes is increasing, a way of predicting which patients with prediabetes are at the highest risk for progressing would be beneficial. Previous studies have examined various factors, but none have been predictive of progression from pre- to type 2 diabetes. Measures of glucose and insulin levels during the oral glucose tolerance test (measured at 1 and 2 hours following a glucose-filled drink) have proven more predictive.

The current study examined the use of the oral glucose tolerance test as a predictor for future type 2 diabetes in patients with prediabetes. This study followed 406 prediabetes patients to determine whether glucose, insulin, or c-peptide (an indicator of insulin production) levels were predictive of type 2 diabetes development. Glucose, insulin, and c-peptide levels were measured at fasting and at 30 and 120 minutes after a glucose drink. Average follow-up time was 46 months, during which time 20% of patients progressed to type 2 diabetes.

Patients with higher fasting blood glucose, higher levels of blood glucose 2-hours after the oral glucose tolerance test and those with impaired glucose tolerance were at a higher risk for developing type 2 diabetes. Comparing patients who progressed from prediabetes to type 2 diabetes to those who did not, HbA1c levels and glucose levels following the oral glucose tolerance test were higher in those who progressed than in patients who did not.

Fasting insulin and c-peptide levels did not differ, but at 30 minutes following the glucose drink, insulin and c-peptide were significantly lower in those who progressed. Patients with glucose levels higher than 165 mg/dL and c-peptide levels lower than 5 ng/dL had 8.83 times the risk of progression to type 2 diabetes compared to those with lower glucose and higher c-peptide levels.

This study concluded that the combination of high glucose and low c-peptide levels at 30 minutes post-glucose tolerance testing is a strong predictor of the progression to type 2 diabetes.

This study was completed only in an Asian population. The strength of this prediction will also need to be explored in other populations.