Insulin secretion based on the late oral glucose tolerance test period and incident diabetes: the San Antonio Heart Study.

ABSTRACT

AIMS: The Insulinogenic Index from 0 to 30 min (ΔI (0-30) /ΔG(0-30) ), a measure of insulin secretion derived from the early period of the oral glucose tolerance test, predicts future diabetes. However, there are few data on secretory measures from the late oral glucose tolerance test period. We therefore investigated the association of the ratio of the area under the insulin curve to the area under the glucose curve from 60 to 120 min (I/G(AUC 60-120) ) with incident diabetes. METHODS: Participants were 1540 Mexican Americans and non-Hispanic whites in the San Antonio Heart Study who were free of diabetes at baseline. We analysed indices of sensitivity (Matsuda index) and secretion from the early (ΔI(0-30) /ΔG(0-30) ) and late oral glucose tolerance test periods (I/G(AUC 60-120) ). RESULTS: A total of 179 participants developed diabetes after 7.5 years. I/G(AUC 60-120) was an independent predictor of diabetes [odds ratio × 1 SD unit increase, 0.37 (0.26-0.54)] in a model that also included age, sex, ethnicity, body mass index, family history of diabetes, Matsuda index and (ΔI (0-30) /ΔG(0-30) ) as covariates. I/G(AUC 60-120) increased the C statistic (a test of discrimination) of the model (0.882 vs. 0.875, P=0.044). I/G(AUC 60-120) correctly reclassified one-fifth of individuals with moderate and strong risks of future diabetes. The net reclassification improvement was 0.13 (P<0.001) and the integrated discrimination improvement was 0.033 (P<0.001). CONCLUSIONS: An insulin secretory measure derived from the late oral glucose tolerance test period is useful for classifying individuals at risk of future diabetes independently of other risk factors, including insulin sensitivity and a secretory measure from the early oral glucose tolerance test period.