REPEATABILITY OF INSULIN SENSITIVITY AND GLUCOSE EFFECTIVENESS FROM THE MINIMAL MODEL - IMPLICATIONS FOR STUDY DESIGN

To determine the repeatability of insulin sensitivity measurements generated by the minimal model, we subjected 11 normal men to 3 frequently sampled intravenous glucose tolerance tests (FSIGTs) over the course of 12 days under conditions of fixed diet and limited physical activity. FSIGTs were analyzed by the minimal model using a full, 30-sample data set, as well as a reduced, 12-sample data set that has been proposed for population studies. Minimal model insulin sensitivity index (S-I) calculated from the 30-sample data set averaged 0.8 +/- 0.083 x 10(-4) min(-1) . (pmol/l)(-1) (range 0.10-1.64 x 10(-4) min(-1) . (pmol/l)(-1) with an average interday coefficient of variation (CV) of 20.2 +/- 3.2% (range 6-44%). Glucose effectiveness (S-G) was slightly less repeatable, with an average interday variability of 25.1 +/- 8.8%. The mean CVs for first-phase insulin secretion (20.1 +/- 3.5%) and total insulin secretion (21.4 +/- 3.2%) were similar to the CV for S-I. Mean insulin sensitivity calculated from the 12-sample data set (0.82 +/- 0.08 x 10(-4) min(-1) . (pmol/l)(-1) was not significantly different from the mean calculated from the full data set (P = 0.37, paired Student's t test). However, the mean CV of S-I calculated from om the reduced data set tended to be greater than that calculated hom the full data set (27.7 +/- 5.4% vs. 20.2 +/- 3.2%). Power calculations using the observed variances from the full and reduced data sets indicated that the full sample protocol is preferable for small studies designed to detect small changes in S-I, whereas the reduced sample protocol is appropriate for studies with large numbers of subjects or large anticipated changes in S-I. Diabetes