INS and diabetes mellitus: Comparison of surrogate indices measuring insulin secretion using OGTT with the gold standard criteria revealed three indices (I30/G30, AUC (I0-30)/AUC (G0-30), first-phase Stumvoll, and Kadowaki model) with the highest Pearson’s and Spearman’s coefficients for both groups (NGT and pre-diabetes) in two phases and during all tests (figure 1).