Measures of β-Cell Function during the Oral Glucose Tolerance Test, Liquid Mixed-Meal Test, and Hyperglycemic Clamp Test

Objective

To evaluate clinically useful measures of β-cell function derived from the oral glucose tolerance test (OGTT) or mixed-meal (ie, Boost) tolerance test to assess insulin secretion in comparison with the gold standard, the hyperglycemic clamp (Hyper-C) test.

Study design

We hypothesized that OGTT/Boost-derived measures are useful estimates of β-cell function and correlate well with insulin secretion measured by the Hyper-C test. This study was designed to assess the correlation between the ratio of the early incremental insulin/glucose responses at 15 and 30 minutes (ΔI₁₅/ΔG₁₅ and ΔI₃₀/ΔG₃₀) of the OGTT and the Boost test with insulin secretion measured during the Hyper-C test (225 mg/dL). The same indices were evaluated using C-peptide. A total of 26 children (14 males, 12 females; mean age, 9.9 ± 0.2 years; mean body mass index = 22.1 ± 1.2 kg/m²) underwent a 2-hour Hyper-C test (225 mg/dL) and 3-hour OGTT and Boost tests with measurements of glucose, insulin, and C-peptide.

Results

Correlations between Hyper-C– and OGTT-derived measures of insulin secretion were stronger for the 15-minute index than for the 30-minute index of insulin secretion and stronger for C-peptide levels than for insulin levels (r = .7, P < .001 for first-phase C-peptide vs both OGTT and Boost, ΔC₁₅/ΔG₁₅).

Conclusions

In children with normal glucose tolerance, C-peptide rather than insulin level measured after 15 minutes of the OGTT or Boost test provides a reliable estimate of β-cell function that correlates well with Hyper-C–derived insulin secretion.

Abbreviations: AUC, Area under the curve, BMI, Body mass index, IGT, Impaired glucose tolerance, NW, Normal weight, OGTT, Oral glucose tolerance test, OW, Overweight, RIA, Radioimmunoassay