Validity and reliability of simple surrogate indexes to evaluate beta-cell function and insulin sensitivity

Background: Simple surrogate indexes (SSI) to assess beta-cell function, insulin sensitivity (IS) and insulin resistance (IR) are an easy and economic tool used in clinical practice to identify glucose metabolism disturbances. Aim: To evaluate the validity and reliability of SSI that estimate beta-cell function, IS and IR using as a reference the parameters obtained from the frequently sampled intravenous glucose tolerance test (FSIVGTT). Material and Methods: We included 62 subjects aged 20-45 years, with a normal body mass index and without diabetes or prediabetes. SSI were compared with the acute insulin response to glucose (AIRg), insulin sensitivity index (Si) and disposition index (DI) obtained from the FSIVGTT using the minimal model approach. Half of the participants (n = 31) were randomly selected for a second visit two weeks later to evaluate the reliability of all the variables. Results: HOMA1-%B and HOMA2-%B had a significant correlation with AIRg (Spearman Rho (r(s)) = 0.33 and 0.37 respectively, p < 0.01). The SSI evaluating IS/IR that showed stronger correlation (r(s) > 0.50) with Si were fasting insulin, HOMA1-IR, HOMA2-IR, HOMA1-%S, HOMA2-%S, QUICKI, and the McAuley index. The parameters that showed good reliability with an intraclass correlation coefficient (ICC) > 0.75 were AIRg, HOMA1-%S, HOMA2-%S, and QUICKI. Conclusions: Our results suggest that most of the SSI are useful and reliable.