Comparison of Second-Phase Insulin Secretion Derived from Standard and Modified Low-Dose Graded Glucose Infusion Tests

Objectives: Insulin secretion has 2 phases, first-phase and second-phase insulin secretion (SPIS). The purpose of our study was to validate the SPIS derived from the modified low-dose graded glucose infusion test (MLDGGI) by using the standard SPIS derived from the low-dose graded glucose infusion test (LDGGI). Methods: Fourteen participants were enrolled. The participants underwent the LDGGI for 200 minutes and MLDGGI for 60 minutes. The LDGGI was administered using the standard Polonsky method, which entails 5 40-minute stages of glucose infusion (1, 4, 8, 6 and 24 mg/kg/min). The slopes of the insulin levels vs. the glucose levels obtained during the test were regarded as SPIS (SPIS-I). Furthermore, deconvolution was performed, and slopes of the insulin secretion rate (ISR) against glucose levels during the test (SPIS-D) were obtained and regarded as the gold standard SPIS. The MLDGGI was administered with 3 20-minute stages of glucose infusion (2, 8 and 24 mg/kg/min) for 20 minutes each. The slopes of the insulin levels vs. the glucose levels obtained during the test were regarded as SPIS (MSPIS-I). In addition, deconvolution was performed, and the slopes of the ISR against glucose levels during the test (MSPIS-D) were obtained. Results: Significant correlations were observed between SPIS-I and SPIS-D (r=0.843; p