An empirical index of insulin sensitivity from short IVGTT: validation against the minimal model and glucose clamp indices in patients with different clinical characteristics.

AIMS/HYPOTHESIS: Minimal model analysis for insulin sensitivity has been validated against the glucose clamp and is an accepted method for estimating insulin sensitivity from IVGTT. However minimal model analysis requires a 3 h test and relevant expertise to run the mathematical model. The aim of this study was to suggest a simple predictor of minimal model analysis index using only 1 h IVGTT.
METHODS: We studied participants with different clinical characteristics who underwent 3 h regular (n = 336) or insulin-modified (n = 160) IVGTT, or 1 h IVGTT and euglycaemic-hyperinsulinaemic clamp (n = 247). Measures of insulin sensitivity were insulin sensitivity index estimated by minimal model analysis (S(I)) and the mean glucose infusion rate (clamp) (M). A calculated S(I) (CS(I)) predictor, CS(I) = Alpha X K(G)/(DeltaAUC(INS)/T), was suggested, based on the calculation of the rate of glucose disappearance K(G) and the suprabasal AUC of insulin concentration DeltaAUC(INS) over T = 40 min. For all the participants, alpha was assumed equal to the regression line slope between K(G)/(DeltaAUC(INS)/T) and S(I) in control participants.
RESULTS: CS(I) and S(I) showed high correlation (R(2) = 0.68-0.96) and regression line slopes of approximately one in the majority of groups. CS(I) tended to overestimate S(I) in type 2 diabetic participants, but results were more reliable when CS(I) was computed with insulin-modified rather than regular IVGTT. CS(I) showed behaviours similar to S(I) as regards relationships with BMI, acute insulin response and sex. CS(I) showed good correlation with M (R(2) = 0.82). CONCLUSIONS/
INTERPRETATION: A short test can achieve a good approximation of minimal model analysis and clamp insulin sensitivity. The importance of a method such as CS(I) is that it allows analysis of IVGTT datasets with samples limited to 1 h.