Measures of beta-cell function during the oral glucose tolerance test, liquid mixed-meal test, and hyperglycemic clamp test.
OBJECTIVE
To evaluate clinically useful measures of beta-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.


METHODS
We hypothesized that OGTT/Boost-derived measures are useful estimates of beta-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 (DeltaI(15)/DeltaG(15) and DeltaI(30)/DeltaG(30)) 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/m(2)) 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, DeltaC(15)/DeltaG(15)).


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 beta-cell function that correlates well with Hyper-C-derived insulin secretion.
Bacha
Fida
F
Division of Pediatric Endocrinology, Metabolism and Diabetes Mellitus, Children's Hospital of Pittsburgh, Pittsburgh, PA 15213, USA.
Gungor
Neslihan
N
Arslanian
Silva A
SA
D002096:C-Peptide / Q000097:blood; D002648:Child; D005260:Female; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test / Q000379:methods*; D006801:Humans; D007328:Insulin / Q000097:blood* / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D050177:Overweight / Q000378:metabolism*; D015203:Reproducibility of Results
D002096:C-Peptide; D007328:Insulin