New insulin sensitivity index from the oral glucose tolerance test

A new insulin sensitivity index was devised on the basis of an autoregressive model and its validity was investigated. Using data from the 75-g oral glucose tolerance test (OGTT), 115 subjects were divided into 3 groups: 40 with normal glucose tolerance, 34 with impaired glucose tolerance, and 41 with type 2 diabetes mellitus. The new insulin sensitivity index: oral glucose insulin sensitivity index (GSI) was calculated from five sets of plasma glucose and insulin levels obtained at 0, 30, 60, 90 and 120 min during OGTT using a formula based on an autoregressive model. Forty-three of the 115 subjects were examined for insulin sensitivity index (ISI) by euglycemic hyperinsulinemic clamp. GSI decreased in the order of normal glucose tolerance group>impaired glucose tolerance group>diabetic group. There was a significant correlation between GSI and the ISI derived from euglycemic hyperinsulinemic clamp study data in all 43 subjects who underwent both tests (r=0.72; P<0.0001). The ISI calculated by previous methods poorly correlated with the ISIs obtained by euglycemic hyperinsulinemic clamp study. In conclusion, this new insulin sensitivity index based on the data obtained from OGTT using an autoregressive model is comparable to an insulin sensitivity index by euglycemic hyperinsulinemic clamp technique and may be superior to previous indexes that have been devised to determine insulin sensitivity from OGTT data.