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155 THE EARLY INSULIN RESPONSE DURING AN ORAL GLUCOSE TOLERANCE TEST EXHIBITS MARKED DAY-TO-DAY VARIABILITY IN FREE-LIVING ADULTS.
  1. K. M. Utzschneider,
  2. J. Tong,
  3. F. Gerchman,
  4. J. Udayasankar,
  5. B. Montgomery,
  6. S. E. Kahn
  1. VA Puget Sound Health Care System and the University of Washington, Seattle, WA

Abstract

The oral glucose tolerance test (OGTT) is often performed in large epidemiology or intervention studies with measures of the early insulin response from this test used to estimate β-cell function. To determine the day-to-day variability of the insulin response and other OGTT measures, we studied 25 healthy adults [10 normal glucose tolerance (NGT), 6 impaired glucose tolerance (IGT) and 9 type 2 diabetes (DM)] with a standard 75 g OGTT performed on two separate days [median 7 days apart (range 5-14 days)]. Subjects were told to follow their same daily routine and to fast overnight. Glucose and insulin were measured at -10, -5, 0, 30, 60, 90. and 120 minutes. Insulin sensitivity was determined by 1/HOMA (22.5/fasting insulin × fasting glucose). The insulin response was determined as the ratio of the change in insulin for the change in glucose over the first 30 minutes (ΔI/ΔG 30 min) and the ratio of the incremental area under the curve from 0-120 minutes for insulin and glucose (incAUCins/incAUCglu). The within subject % coefficient of variation (CV) was computed.

Results None of the OGTT variables or weight differed significantly between the study days. Each variable on study day 1 was highly correlated with the same variable on study day 2 (r = .89-.99, p < .001). CVs were not significantly different between glucose tolerance categories.

Table

% CVs for OGTT Variables

Conclusions The early insulin response (ΔI/ΔG 30 min) during the OGTT shows marked within-subject variability from day to day. Studies that use this as a measure of β-cell function need to take this variability into account when calculating sample size.

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