The disposition index does not reflect β-cell function in IGT subjects treated with pioglitazone

Abstract

Aims and Hypothesis: The insulin secretion/insulin resistance (IR) (disposition) index (ΔI/ΔG ÷ IR, where Δ is change from baseline, I is insulin, and G is glucose) is commonly used as a measure of (3-cell function. This relationship is curvilinear and becomes linear when log transformed. ΔI is determined by 2 variables: insulin secretion rate (ISR) and metabolic clearance of insulin. We postulated that the characteristic curvilinear relationship would be lost if Δ plasma C-peptide(ACP) (instead of Δ plasma insulin) was plotted against insulin sensitivity. Methods: A total of 441 individuals with impaired glucose tolerance (IGT) from ACT NOW received an oral glucose tolerance test and were randomized to pioglitazone or placebo for 2.4 years. Results: Pioglitazone reduced IGT conversion to diabetes by 72% (P