UNDERSTANDING ORAL GLUCOSE-TOLERANCE - COMPARISON OF GLUCOSE OR INSULIN MEASUREMENTS DURING THE ORAL GLUCOSE-TOLERANCE TEST WITH SPECIFIC MEASUREMENTS OF INSULIN-RESISTANCE AND INSULIN-SECRETION

The extent to which the oral glucose tolerance test can be used to est imate insulin secretion and insulin resistance has been evaluated by c omparing glucose and insulin concentrations during an oral glucose tol erance test with specific measurements of insulin secretion and insuli n resistance in 85 normoglycaemic subjects and 23 subjects with impair ed glucose tolerance (IGT). Insulin secretion was measured by the firs t phase insulin response to intravenous glucose and insulin resistance by the insulin tolerance test which measures the decline of plasma gl ucose after the injection of a bolus of insulin. The best measure of i nsulin secretion was the ratio of the 30 min increment in insulin conc entration to the 30 min increment in glucose concentration following o ral glucose loading. This correlated with the first phase insulin rele ase following intravenous glucose (r = 0.61, p < 0.001) but not insuli n resistance (r = -0.05, p > 0.05). Insulin resistance could be estima ted by the fasting insulin, proinsulin, or split proinsulin concentrat ions. However, fasting split proinsulin appeared to discriminate best between insulin resistance (r = -0.53, p < 0.001) and insulin secretio n (r = 0.07, p > 0.05). Relative insulin resistance estimated by homeo stasis model assessment (HOMA), also correlated well with insulin resi stance (r = -0.57, p < 0.001) but not insulin secretion (r = 0.01, p > 0.05). We conclude that the oral glucose tolerance test can be used t o derive estimates of the relative roles of insulin secretion and insu lin resistance in population studies of glucose tolerance.