Oral Glucose Tolerance Test Indexes for Insulin Sensitivity and Secretion Based on Various Availabilities of Sampling Times

We have recently proposed a series of indexes for β-cell function and insulin sensitivity to be calculated from glucose and insulin concentrations obtained during a classic World Health Organization oral glucose tolerance test (OGTT) (1). The models were validated by the euglycemic-hyperinsulinemic and the hyperglycemic clamp technique, respectively. The generation of these indexes was based on simple statistical models using stepwise linear regression analysis. The variables in the model assumed the availability of determinations at 0, 30, 60, 90, and 120 min. Since the publication of this article, we have been contacted repeatedly by potential users of the indexes who do not have at their disposal all of the time points required for the various indexes.

Therefore, we returned to the original database of OGTTs and euglycemic and hyperglycemic clamps in the 104 nondiabetic subjects (normal glucose tolerance, n = 65; impaired glucose tolerance, n = 39) and generated the equations for different sets of time points. The exact same procedures were applied as previously described (1), except the indicated variables only were entered in the model. The equations were generated using both pure OGTT data and OGTT data plus demographic data (BMI, age, and waist-to-hip ratio). The resulting equations with the variables remaining in the equations are shown in Tables 1 and 2. The r values for the insulin secretion parameters ranged from 0.65 to 0.79 and for insulin sensitivity from 0.59 to 0.79. For comparison, the homeostasis model assessment (HOMA) resistance index was reasonably well correlated with the insulin sensitivity index (r = −0.59, P < 0.001) and the metabolic clearance rate (r = −0.56, P < 0.001), and the HOMA secretion index was reasonably well correlated with first-phase (r = 0.57, P < 0.001) and second-phase insulin release (r = 0.62, P < 0.001), as previously reported (1).

In conclusion, given many variations in oral glucose tolerance, reasonable estimates for insulin secretion and insulin sensitivity can be made. The optimal sampling constellation appears to be 0, 30, and 120 min, including age and BMI (all r values >0.78).