Comparative evaluation of simple insulin sensitivity methods based on the oral glucose tolerance test

We compared five surrogate insulin sensitivity (IS) methods against the euglycaemic-hyperinsulinaemic clamp. These methods were the homeostasis model assessment (HOMA) and four methods based on the OGTT (OGIS, MCRest, ISIcomp, SIORAL).

We compared these IS methods against the clamp (0.28 nmol.min(-1).m(-2) insulin infusion) M value in 147 women (58-61 years; BMI 19-38 kg/m2; 116 NGT, 25 IFG/IGT, six type 2 diabetic), by evaluating the correlation coefficient with M. We also tested the ability to reproduce the relationships between IS and typical IS correlates (BMI, fasting insulin, insulin to glucose OGTT area ratio and fasting, 2 h and mean glucose) by means of the "discrepancy index" D, in which (1) D=0 if the correlation between IS and the variable of interest is as with the clamp, (2) D is smaller than 0 if the correlation is overestimated, and (3) D is greater than 0 if underestimated.

All IS methods correlated with M (r=0.57-0.83, p<0.0001); for MCRest the relationship was markedly curvilinear. All IS measures correlated with the considered variables (r=0.29-0.94, p<0.0005); however, no method had D approximately 0 for all variables. The best surrogates of M were OGIS (one D not =0) and MCRest (two D not =0); the other methods either under- or overestimated the degree of correlation (three or more D not =0), in particular with fasting insulin (HOMA: D=-57%; ISIcomp: D=-36%) and BMI (HOMA: D=-14%; ISIcomp: D=-14%; SiORAL: D=-11%).

All IS methods were correlated with M. OGIS and MCRest were preferable to the other methods and in particular to HOMA for reproducing relationships with the independent variables.