Comparison of a radioimmunoassay with a microparticle enzyme immunoassay of insulin for use with the minimal model method of determining whole-body insulin sensitivity.

The purpose of this study was to compare minimal model results of insulin sensitivity and glucose effectiveness using insulin levels measured by a conventional radioimmunoassay (RIA) versus an automated microparticle enzyme immunoassay (MEIA). Thirty obese subjects participated in an insulin-modified frequently sampled intravenous glucose tolerance test. The MEIA exhibited lower day-to-day variability than did the RIA. The MEIA yielded lower insulin values compared to the RIA probably because of the high cross-reactivity with proinsulin in the RIA. The MEIA yielded a good correlation with the RIA for both insulin sensitivity (r = 0.97, p = 0.0001) and for glucose effectiveness (r = 0.98, p = 0.0001). The MEIA did not significantly effect the results of the MinMod analysis and the low cross-reactivity with proinsulin makes MEIA preferable when insulin sensitivity (SI) is measured in patients with diabetes or obese individuals whose insulin:proinsulin ratio is altered.