Determining pancreatic β-cell compensation for changing insulin sensitivity using an oral glucose tolerance test

Plasma glucose, insulin, and C-peptide responses during an OGTT are informative for both research and clinical practice in type 2 diabetes. The aim of this study was to use such information to determine insulin sensitivity and insulin secretion so as to calculate an oral glucose disposition index (DIOGTT) that is a measure of pancreatic beta-cell insulin secretory compensation for changing insulin sensitivity. We conducted an observational study of n = 187 subjects, representing the entire glucose tolerance continuum from normal glucose tolerance to type 2 diabetes. OGTT-derived insulin sensitivity (S-I OGTT) was calculated using a novel multiple-regression model derived from insulin sensitivity measured by hyper-insulinemic euglycemic clamp as the independent variable. We also validated the novel S-I OGTT in n = 40 subjects from an independent data set. Plasma C-peptide responses during OGTT were used to determine oral glucose-stimulated insulin secretion (GSIS(OGTT)), and DIOGTT was calculated as the product of S-I OGTT and GSIS(OGTT). Our novel S-I OGTT showed high agreement with clamp-derived insulin sensitivity (typical error = + 3.6%; r = 0.69, P < 0.0001) and that insulin sensitivity was lowest in subjects with impaired glucose tolerance and type 2 diabetes. GSIS(OGTT) demonstrated a significant inverse relationship with S-I OGTT. GSIS(OGTT) was lowest in normal glucose-tolerant subjects and greatest in those with impaired glucose tolerance. DIOGTT was sequentially lower with advancing glucose intolerance. We hereby derive and validate a novel OGTT-derived measurement of insulin sensitivity across the entire glucose tolerance continuum and demonstrate that beta-cell compensation for changing insulin sensitivity can be readily calculated from clinical variables collected during OGTT.