Postprandial C-peptide to glucose ratio as a predictor of β-cell function and its usefulness for staged management of type 2 diabetes

Aims/Introduction: Type 2 diabetes is characterized by progressive deterioration of β-cell function. Recently, it was suggested that the C-peptide-to-glucose ratio after oral glucose ingestion is a better predictor of β-cell mass than that during fasting. We investigated whether postprandial C-peptide-to-glucose ratio (PCGR) reflects β-cell function, and its clinical application for management of type 2 diabetes. Materials and Methods: We carried out a two-step retrospective study of 919 Korean participants with type 2 diabetes. In the first step, we evaluated the correlation of PCGR level with various markers for β-cell function in newly diagnosed and drug-naïve patients after a mixed meal test. In the second step, participants with well-controlled diabetes (glycated hemoglobin <7%) were divided into four groups according to treatment modality (group I: insulin, group II: sulfonylurea and/or dipeptityl peptidase IV inhibitor, group III: metformin and/or thiazolidinedione and group IV: diet and exercise group). Results: In the first step, PCGR was significantly correlated with various insulin secretory indices. Furthermore, PCGR showed better correlation with glycemic indices than homeostatic model assessment of β-cell function (HOMA-β). In the second step, the PCGR value significantly increased according to the following order: group I, II, III, and IV after adjusting for age, sex, body mass index and duration of diabetes. The cut-off values of PCGR for separating each group were 1.457, 2.870 and 3.790, respectively (P < 0.001). Conclusions: We suggest that PCGR might be a useful marker for β-cell function and an ancillary parameter in the choice of antidiabetic medication in type 2 diabetes.