Minimal-model estimates of insulin sensitivity are insensitive to errors in glucose effectiveness

The minimal-model method allows for estimation of insulin sensitivity (S-I = P-3/P-2) and glucose effectiveness (S-G = P-1) from the time course of gl ucose and insulin after a glucose bolus. We previously demonstrated that th e minimal-model results in overestimates of S-G in subjects with normal ins ulin secretory function. To determine whether overestimation of S-G has an impact on estimation of S-I, we examined model estimation of S-I when S-G w as constrained to levels below that found by the regular minimal-model fit. Fifty-six glucose tolerance tests from lean and obese women, with and with out polycystic ovary syndrome, were used. S-I ranged from 0.2-22.6 X 10(-4) min(-1)/(mu U/mL), and S-G ranged from 0.8-3.8 x 10(-2) min(-1) for the st andard minimal-model fits. Constraining S-G to as low as 40% of the unconst rained value resulted in a 4-fold increase in P-2 and P-3, but only a 3% re duction in S-I. We conclude that estimation of the insulin sensitivity inde x is independent of errors in minimal-model-derived estimates of glucose ef fectiveness.