Estimating insulin secretion in youth using simple indices derived from the oral glucose tolerance test

Abstract

Simple estimates of insulin secretion feasible for large epidemiological studies have been proposed in adults, but have been little evaluated in young people. For this reason, this study examined the correlation between OGTT-derived and fasting-based indices of insulin secretion against the acute insulin response to glucose (AIRg) in children. Twenty subjects (nine boys and 11 girls; mean [SD] age: 9 [2] years) were studied. Their mean (SD) BMI Z score was 1.5 (0.8). All participants had normal fasting and 2-h post-load glucose. Each subject underwent an insulin-modified minimal model frequently sampled intravenous glucose tolerance test (FSIVGTT) as the reference method, and a 3-h OGTT. AIRg was computed from the FSIVGTT. A total of ten indices were calculated using OGTT data, while HOMA%beta (original formula) and HOMA2%beta (computer-based) were computed from fasting samples. Correlations were established using Spearman's rank correlations. Of the ten indices derived from the OGTT, those most closely correlated with the AIRg (using FSIVGTT) included the insulinogenic index(t30)(min) (r = 0.80), insulin/glucose ratio(t30)(min) (r = 0.71) and ratio of the area under the curve for insulin to glucose(t0-30)(min) (r = 0.74). Both the HOMA%beta and HOMA2%beta correlated modestly with AIRg (r = 0.62 and r=0.65, respectively). Our results suggest that OGTT-derived measures of insulin secretion provide adequate estimates of first-phase insulin secretion in youth. HOMA2%beta and HOMA%beta represent acceptable compromises, although HOMA2%beta may be preferable in younger individuals, as it allows for a wider spectrum of insulin and glucose values that are physiological in this age group.