Measuring b-Cell Function Relative to Insulin Sensitivity in Youth Does the hyperglycemic clamp suffice?

OBJECTIVEdTo compare b-cell function relative to insulin sensitivity, disposition index (DI), calculated from two clamps (2cDI, insulin sensitivity from the hyperinsulinemic-euglycemic clamp and first-phase insulin from the hyperglycemic clamp) with the DI calculated from the hyperglycemic clamp alone (hcDI). RESEARCH DESIGN AND METHODSdComplete data from hyperglycemic and hyperinsulinemic-euglycemic clamps were available for 330 youth: 73 normal weight, 168 obese with normal glucose tolerance, 57 obese with impaired glucose tolerance, and 32 obese with type 2 diabetes. The correlation between hcDI and 2cDI and Bland-Altman analysis of agreement between the two were examined. RESULTSdInsulin sensitivity and first-phase insulin from hcDI showed a hyperbolic relation-ship. The hcDI correlated significantly with 2cDI in the groups combined (r = 0.85, P, 0.001) and within each group separately (r $ 62, P, 0.001). Similar to 2cDI, hcDI showed a declining pattern of b-cell function across the glucose-tolerance groups. Overall, hcDI values were 27% greater than 2cDI, due to the hyperglycemic versus euglycemic conditions, reflected in a positive bias with Bland-Altman analysis