New insights on the simultaneous assessment of insulin sensitivity and beta-cell function with the HOMA2 method.

The homeostasis model assessment (HOMA) is a method for assessing -cell function and insulin sensitivity that has gained widespread use thanks to its simplicity and validity (1). The method has recently been reviewed by the group of investigators that championed its development (2). They pointed out that -cell function cannot be interpreted without the knowledge of insulin sensitivity, and, thus, HOMA of insulin sensitivity (HOMA-S%) should always be reported alongside HOMA of -cell function (HOMA-B%). Unfortunately, and more often than not, the HOMA indexes are not calculated in tandem. In fact, Wallace et al. (2) observed that in 75% of articles adopting the HOMA method, only HOMA-S% was reported. This is disappointing, since evidence has been accumulating that insulin sensitivity and -cell function are inextricably linked and should be measured simultaneously because their interplay is fundamental to glucose tolerance. In 1979, Turner et al. (3) disclosed the existence of a curvilinear relationship between the indexes of insulin resistance and -cell deficiency, which was estimated with a mathematical model of the glucose-insulin feedback loop (a precursor of the HOMA method). In 1981, Bergman et al.(4) showed the presence of a similar relationship between the indexes of insulin sensitivity and -cell function obtained from the intravenous glucose tolerance test with the minimal model. They also introduced the disposition index (DI), the product of insulin sensitivity times -cell function, showing that this summary measure was associated with the glucose tolerance displayed during the intravenous glucose tolerance test. These concepts were thoroughly analyzed by Kahn et al. (5), who showed that when insulin sensitivity and secretion are plotted together, a hyperbolic relationship can be observed in healthy humans of varying degree of obesity. Since graphical representation and DI have received considerable attention in recent years (6–10), we thought that they could be profitably applied to the HOMA method. In the following, we report some observations supporting the view that the joint use of HOMA indexes enhances the appeal of HOMA method.