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Reproducibility of the Oral Glucose Tolerance Test in Overweight Children

Divisions of Pediatric Endocrinology, Metabolism and Diabetes Mellitus, and Weight Management and Wellness (I.M.L., A.B., S.A.), Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania 15213; and Department of Epidemiology (E.B.-M.), Graduate School of Public Health, and Center for Exercise and Health-Fitness Research (R.R.), University of Pittsburgh, Pittsburgh, Pennsylvania 15260

Address all correspondence and requests for reprints to: Ingrid M. Libman, M.D., Ph.D., Children’s Hospital of Pittsburgh, 3705 Fifth Avenue, 4th A De Soto Wing, Pittsburgh, Pennsylvania 15213. E-mail: ingrid.libman{at}chp.edu.

Objective: We examined the reproducibility of the oral glucose tolerance test (OGTT) in overweight children and evaluated distinguishing characteristics between those with concordant vs. discordant results.

Design: Sixty overweight youth (8–17 yr old) completed two OGTTs (interval between tests 1–25 d). Insulin sensitivity was assessed by the surrogate measures of fasting glucose to insulin ratio, whole-body insulin sensitivity index, and homeostasis model assessment of insulin resistance, and insulin secretion by the insulinogenic index with calculation of the glucose disposition index (GDI).

Results: Of the 10 subjects with impaired glucose tolerance (IGT) during the first OGTT only three (30%) had IGT during the second OGTT. The percent positive agreement between the first and second OGTT was low for both impaired fasting glucose and IGT (22.2 and 27.3%, respectively). Fasting blood glucose had higher reproducibility, compared with the 2-h glucose. Youth with discordant OGTTs, compared with those with concordant results, were more insulin resistant (glucose/insulin 2.7 ± 1.4 vs. 4.1 ± 1.8, P = 0.006, whole-body insulin sensitivity index of 1.3 ± 0.6 vs. 2.2 ± 1.1, P = 0.003, and homeostasis model assessment of insulin resistance 10.6± 8.1 vs. 5.7 ± 2.8, P = 0.001), had a lower GDI (0.45 ± 0.58 vs. 1.02 ± 1.0, P = 0.03), and had higher low-density lipoprotein cholesterol (117.7 ± 36.6 vs. 89.9 ± 20.1, P = 0.0005) without differences in physical characteristics.

Conclusions: Our results show poor reproducibility of the OGTT in obese youth, in particular for the 2-h plasma glucose. Obese youth who have discordant OGTT results are more insulin resistant with higher risk of developing type 2 diabetes mellitus, as evidenced by a lower GDI. The implications of this remain to be determined in clinical and research settings.

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