Evaluation of proposed oral disposition index measures in relation to the actual disposition index

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Abstract
Aims While the disposition index provides a useful measure of B‐cell function, its calculation requires the performance of a frequently sampled intravenous glucose tolerance test (FSIVGTT). Recently, the demonstration of a hyperbolic relationship between indices of insulin secretion and insulin sensitivity derived from the oral glucose tolerance test (OGTT) has led to the introduction of two novel OGTT‐based measures of B‐cell function analogous to the disposition index: (i) the insulin secretion‐sensitivity index‐2 (ISSI‐2) (defined as the ratio of the area‐under‐the‐insulin‐curve to the area‐under‐the‐glucose curve, multiplied by the Matsuda index) and (ii) insulinogenic index (IGI)/fasting insulin. However, neither of these two measures has been directly compared with the disposition index. Methods Two hundred and thirteen non‐diabetic children (122 boys, 91 girls) underwent both OGTT and FSIVGTT, allowing for the calculation of ISSI‐2, IGI/fasting insulin and the disposition index. Results ISS1‐2 and IGI/fasting insulin were strongly correlated with each other (r = 0.82, P < 0.0001). Both measures correlated with the disposition index, with ISSI‐2 showing a modestly stronger association (ISSI‐2: r = 0.24, P = 0.0003; IGI/fasting insulin: r = 0.21, P = 0.0022). Standardized linear regression analyses confirmed that the relationship between log ISSI‐2 and the disposition index (standardized regression coefficient = 0.224, P = 0.001) was stronger than that between log IGI/fasting insulin and the disposition index (standardized regression coefficient = 0.166, P = 0.015). Conclusions The OGTT‐derived measures ISSI‐2 and IGI/fasting insulin exhibit modest correlations with the disposition index. These relationships require further assessment in other patient populations.