Muscle and Liver Insulin Resistance Indexes Derived From the Oral Glucose Tolerance Test

OBJECTIVE—To derive indexes for muscle and hepatic insulin sensitivity from the measurement of plasma glucose and insulin concentrations during an oral glucose tolerance test (OGTT). RESEARCH DESIGN AND METHODS—A total of 155 subjects of Mexican-American origin (58 male and 97 female, aged 18–70 years, BMI 20–65 kg/m2) with normal glucose tolerance (n = 100) or impaired glucose tolerance (n = 55) were studied. Each subject received a 75-g OGTT and a euglycemic insulin clamp in combination with tritiated glucose. The OGTT-derived indexes of muscle and hepatic insulin sensitivity were compared with hepatic and muscle insulin sensitivity, which was directly measured with the insulin clamp, by correlation analysis. RESULTS—The product of total area under curve (AUC) for glucose and insulin during the first 30 min of the OGTT (glucose0–30[AUC] × insulin0–30[AUC]) strongly correlated with the hepatic insulin resistance index (fasting plasma insulin × basal endogenous glucose production) (r = 0.64, P < 0.0001). The rate of decay of plasma glucose concentration from its peak value to its nadir during the OGTT divided by the mean plasma insulin concentration (dG/dt ÷ I) strongly correlated with muscle insulin sensitivity measured with the insulin clamp (P = 0.78, P < 0.0001). CONCLUSIONS—Novel estimates for hepatic and muscle insulin resistance from OGTT data are presented for quantitation of insulin sensitivity in nondiabetic subjects.