Misclassification of subjects with insulin resistance and associated cardiovascular risk factors by homeostasis model assessment index. Utility of a postprandial method based on oral glucose tolerance test

Different methods are available for assessing insulin sensitivity in the fasting state. However, insulin resistance (IR) is initially a postprandial disturbance; and usually, when basal (fasting) disturbance appears, the process has been in progress for some time. Our aim was to investigate if a postprandial measurement, performing an oral glucose tolerance test (OGTT), is more sensitive than fasting values. We wished to identify early IR states in healthy, nonobese individuals and ascertain if this situation was associated with other cardiovascular risk factors. A total of 90 nonobese, nondiabetic, and nonsmoker individuals were studied. They were divided into 3 groups according to IR state—group 1: non-IR—homeostasis model assessment of IR (HOMAIR) and insulin sensitivity index of Matsuda-De Fronzo (ISI-Mat) were normal (HOMAIR <3.2 and ISI-Mat >4.0); group 2: with IR post-OGTT (ISI-Mat ≤4.0 and HOMAIR <3.2); and group 3: subjects with IR in basal conditions (HOMAIR ≥3.2). An intravenous glucose tolerance test to compare both indices was also performed. In 14.4% of subjects, the fasting HOMAIR values failed to identify IR (false-negative results). The ISI-Mat values were better correlated than HOMAIR (r = 0.875, P = .0001 and r = −0.631, P = .0001, respectively) with insulin sensitivity index obtained with intravenous glucose tolerance test. Subjects with IR had higher prevalence of a cluster of cardiovascular risk factors than non-IR subjects. These data show that that a significant percentage of subjects were misclassified with HOMAIR. Early identification of IR by OGTT was associated with other cardiovascular risk factors. The OGTT is a simple method that could be applied to accurately identify IR subjects in the general population.