Onset of type 2 diabetes (T2D) is based on the insulin secretion (loss of β-cell function) and resistance. Residual β-cell function is a key factor in achieving optimal glycemic control in T2D patients. Glucagon stimulates insulin, therefore glucagon stimulation test (GST) is a reliable marker for β-cell function. Fasting C-peptide (CPR) to glucose ratio (CPR[ng/ml] to glucose[mg/dl] x100; F-CPR-index) is used as a marker of insulin secretion. We evaluated the efficacy of postprandial CPR to glucose ratio (P-CPR-index) for evaluating β-cell function in T2D. Japanese T2D patients with inadequate glycemic control (HbA1c>7.0) were enrolled in the study (n=500, insulin therapy=283). HbA1c, fasting CPR and glucose, postprandial (120 min after breakfast) CPR and glucose were measured, and F-CPR-index and P-CPR-index were calculated. GST was performed as follows: 1mg of glucagon was injected intravenously, CPR was determined before and 6 min after injection, GSTΔCPR (CPR[6 min] - CPR[0 min]) was calculated. Factors correlated with GSTΔCPR were analyzed using simple and multiple stepwise regression analysis. P value<0.05 was defined as statistically different. F-CPR-index, P-CPR-index and GSTΔCPR were 1.60±0.95, 2.67±1.92 and 1.93±1.21, respectively. Simple regression analysis showed that GSTΔCPR was significantly correlated with age, height, body weight (BW), BMI, waist circumference, duration of diabetes, retinopathy, insulin therapy, urinary CPR, F-CPR-index and P-CPR-index. Multiple stepwise regression analysis revealed that independent factors contributing to GSTΔCPR were BW (β=0.336), duration of diabetes (β= −0.107), presence of retinopathy (β= −0.121), use of DPP-4i (β= −0.099), metformin (β= −0.109), SGLT2i (β= −0.108, p=0.002) and P-CPR-index (β=0.432)(R2=0.453). Our date demonstrated that P-CPR-index was valuable and simple method in assessing residual β-cell function with/without insulin therapy in daily clinical practice.


Y.Matsuhashi: None. T.Abe: None. T.Fujita: None. S.Mizushiri: None. S.Chikazawa: None. M.Daimon: None.

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