INSULIN SENSITIVITY AND GLUCOSE EFFECTIVENESS - MINIMAL MODEL ANALYSIS OF REGULAR AND INSULIN-MODIFIED FSIGT

The minimal model is widely used to evaluate insulin action on glucose disappearance from frequently sampled intravenous glucose tolerance t ests (FSIGT). The common protocols are a regular (rFSIGT, single injec tion of 0.3 g/kg of glucose) and an insulin-modified test (mFSIGT, wit h an additional insulin administration at 20 min). This study compared the insulin sensitivity index (S-I) and glucose effectiveness (S-G) O btained in the same individual (16 normal subjects) with the two tests . S-I was 7.11 +/- 0.80 10(-4).min(-1).mu U-1.ml in rFSIGT and 6.96 +/ - 0.83 in mFSIGT (P = 0.656), regression r = 0.92, P < 0.0001; S-G was 0.0260 +/- 0.0028 min(-1) and 0.0357 +/- 0.0052, respectively, statis tically different (P = 0.013) but still with a good regression (r = 0. 66, P = 0.0051). S-G and insulin amount during the early period correl ated (r = 0.6, P = 0.015 in rFSIGT and r = 0.76, P = 0.0006 in mFSIGT) . In summary, both FSIGTs with minimal model analysis provide the same S-I, which is a very robust index. S-G was different by 28% due proba bly to the relationship between S-G and the amount of circulating insu lin. In studies comparing groups, the simpler rFSIGT can still be used with the advantage of accounting for endogenous insulin, thus offerin g the possibility of direct inferences on the beta-cell activity.