Abstract

In a previous work of our group the “I0*G60” -a novel predictor of Insulin Resistance (IR)-, was found when we performed a ROC analysis of several biochemical predictors of IR, including the Matsuda-DeFronzo’s Insulin Sensitivity Index test, ISI) against the Pancreatic Suppression Test (PST). ROC analysis defined the optimal diagnostic cut-offs of several biochemical predictors of IR, including the ISI. The I0*G60 is the product of the I0 (fasting serum insulin value) times the G60 (serum glucose value at 60 minutes of the OGTT). In 90 subjects having both a PST and an OGTT, the I0*G60 outperformed all the studied predictors of IR. The ISI value was calculated in Matsuda's webpage (ISI-OL). The I0*G60 and the ISI-OL were linearly correlated (r = -0.627). In this work, we plotted the I0*G60 against the ISI-OL in the initial cohort of 90 subjects. The graph was highly suggestive of a rectangular hyperbolic relationship between these two predictors. We, therefore, modelled the relationship as a non-linear regression and obtained an equation describing the I0*G60-based prediction of the ISI-OL: ISI-OL = parameter1* “I0*G60” ^ parameter2. The non-linear determination coefficient (r²) was 0.899. We repeated the procedure with a total of 831 pair of values. The linear correlation coefficient between these variables was -0.573. The resulting graph was again highly suggestive of a rectangular hyperbolic relationship. The modelling produced the final predictive equation: ISI-OL = 782.7 * “I0*G60” ^ - 0.744. The determination coefficient (r²) was 0.822. We conclude that the main reason for the excellent performance of the I0*G60 resides in its ability to accurately predict the ISI-OL value.

Keywords: Predictors of Insulin Resistance; ISI-Composite; I0*G60; Hyperbolic Rectangular Relationship

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