Natural history of impaired glucose tolerance: follow-up at Joslin Clinic.

The goal of this study was to examine follow-up data on the offspring of two parents with NIDDM who have IGT to identify predictors of progression to NIDDM. The study group consisted of 80 individuals with IGT (WHO criteria), 28 of whom had IGT at baseline, and 52 who developed it during follow-up. Both an oral glucose tolerance test (OGTT) and an intravenous glucose tolerance test (IVGTT) were performed at baseline. After a median follow-up interval of 8 years, 35% had progressed to NIDDM, 37% had reverted to normal glucose tolerance, and 29% still had IGT. Those who progressed were younger and more obese than non-progressors. Glucose and insulin values from the OGTT that established the diagnosis of IGT were analysed by multiple logistic regression to determine which time points best discriminated between progressors and non-progressors. High insulin, but not glucose, values at 0 and 120 min distinguished progressors from non-progressors. Values at other sample times that were significantly different (p < 0.05) in progressors were: higher glucose values at 30, 45, and 60 min and higher insulin values at 90 and 180 min. Multiple logistic regression analysis of Bergman's minimal model parameters obtained from the IVGTTs performed at baseline demonstrated that, once IGT is established, low acute phase insulin secretion as well as low insulin sensitivity are significant predictors of progression to NIDDM.