Comparison of tests of B-cell function across a range of glucose tolerancefrom normal to diabetes

Adequate comparisons of the relative performance of different tests of beta -cell function are not available. We compared discrimination of commonly us ed in vivo tests of beta-cell function across a range of glucose tolerance in seven subjects with normal glucose tolerance (NGT), eight subjects with impaired glucose tolerance (IGT), and nine subjects with type 2 diabetes. I n random order, each subject underwent two of each of the following tests: 1) frequently sampled 0.3-g/kg intravenous glucose tolerance test (FSIVGTT) with MinMod analysis; 2) homeostasis model assessment CHOMA) from three sa mples at 5-min intervals with a model incorporating immunoreactive or speci fic insulin measurements; and 3) continuous infusion of 180 mg . min(-1) . m(-2) glucose with model assessment (CIGMA) of three samples at 50, 55, and 60 min(1-h CIGMA) and at 110, 115, and 120 min (2-h CIGMA). The discrimina tion of each test was assessed by the ratio of the within-subject SD to the underlying between-subject SD, the discriminant ratio (DR). The degree to which tests measured the same physiological variable was assessed using Pea rson's correlation coefficient adjusted for attenuation due to test impreci sion. An unbiased line of equivalence, taking into account the imprecision of both tests, was used to compare results. beta-Cell function assessed fro m HOMA and beta-cell function assessed from CIGMA (CIGMA%beta) (using immun oreactive insulin) had higher DRs than first-phase intravenous glucose tole rance test-derived incremental insulin peak, area, insulin-to-glucose index , and acute insulin response to glucose from FSIVGTT-MinMod. CIGMA%beta (im munoreactive insulin) had the highest DR. FSIVGTT-derived first-phase insul in response tests correlated only moderately with BOMA and CIGMA. Using spe cific rather than immunoreactive insulin for HOMA and CIGMA did not improve discriminatory power. Simple tests such as HOMA and CIGMA, using immunorea ctive insulin, offer better beta-cell function discrimination across subjec ts with NGT, IGT, and type 2 diabetes than measurements derived from FSIVGT T first-phase insulin response.