Reproducibility of the Oral Glucose Tolerance Test in Overweight Children

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. (J Clin Endocrinol Metab 93: 4231-4237, 2008)