Evaluation of second phase insulin secretion with simple surrogates derived from the mixed meal tolerance test in...

The major contributors to the pathogenesis of type 2 diabetes are impaired insulin action and insulin secretion, including second phase insulin secretion (2nd ISEC). This study aimed to compare surrogates derived from the mixed meal tolerance test (MTT) with 2nd ISEC derived from modified low-dose graded glucose infusion (M-LDGGI) in patients with type 2 diabetes. We were subsequently able to decide which surrogate would be performed easily and accurately. Twenty type 2 diabetes patients were enrolled. They received both MTT and M-LDGGI. The standardized MTT meals were provided at 8:00 A.M. and 12:00 P.M. The M-LDGGI was a simplified version of the Polonsky method; only two 80-min stages of glucose infusion (2 and 6 mg/kg/min) were given. The slopes of the insulin to glucose curve during the test were regarded as the 2nd ISEC. First, we used the area under the insulin curve (AUC(IN)) during MTT to quantify the 2nd ISEC. The best correlated AUC(IN) was from 60-240 min. Second, the slopes between any two time points of the plasma insulin to glucose level (SLOPE(I/G)) were also assessed. The time period best correlated with 2nd ISEC was from 0-120 min (SLOPE₀₋₁₂₀). Finally, the insulin-to-glucose ratio (IGr) of each time point was used to estimate the 2nd ISEC, and the best correlation was observed at 180 min. In conclusion, estimating 2nd ISEC surrogates derived from MTT proved to be possible. The most accurate surrogate is the SLOPE₀₋₁₂₀, while IG(r180) is another less precise but more convenient method.