Comparison of three methods for the quantification of beta-cell function and insulin sensitivity.

The purpose of this study was to compare two techniques for the quantification of beta-cell function and insulin sensitivity. Sixteen subjects (2 with newly diagnosed non-insulin-dependent diabetes mellitus, 8 with impaired glucose tolerance (IGT) and 6 with normal glucose tolerance (NGT)), aged 40-65 years underwent an oral glucose tolerance test (OGTT), a continuous infusion of glucose with model assessment (CIGMA) and a hyperglycaemic clamp (10 mmol/l) in random order. As measures of beta-cell function we used the clamp derived area under the curve from 0-10 min (first phase insulin response) and the mean insulin level during the last 20 min of the clamp (second phase insulin response). Insulin sensitivity was reflected by the ratio of the glucose infusion rate and the mean insulin level during the last 20 min of the clamp (M/I ratio). Measures for beta-cell function and insulin sensitivity derived from OGTT and CIGMA appeared to correlate only moderately (0.5-0.7) with the corresponding clamp measures. It is concluded that OGTT and CIGMA derived measures of beta-cell function and insulin sensitivity should be interpreted with caution.