OGTT 2-hour serum C-peptide index as a predictor of post-transplant diabetes mellitus in kidney transplant recipients

Background: The high incidence of post-transplant diabetes mellitus (PTDM) necessitates the identification of new factors to explain its pathogenesis. This study aimed to clarify the association between the C-peptide index (CPI) and PTDM. Methods: A total of 290 non-diabetic kidney transplant patients were analyzed. All subjects underwent a 75 g oral glucose tolerance test (OGTT). Plasma glucose concentrations, serum C-peptide levels, hemoglobin A1c (HbA1c), and other biochemical indicators were measured. CPI was calculated as the ratio of serum C-peptide to plasma glucose. Results: Among the 290 patients, 36 (12.4%) developed PTDM at the end of 1 year. Patients with PTDM had older age (P<0.001), higher levels of body mass index (BMI) (P=0.004) and HbA1c (P=0.001), a higher proportion of deceased donors (P=0.045), and lower levels of 2 h-CPI (P=0.02) than those without PTDM. The OGTT 2 h-CPI was positively correlated with BMI, HbA1c, type of calcineurin inhibitor, albumin, and triglyceride. Multivariate logistic regression and Cox hazard model analysis showed that pre-transplant OGTT 2 h-CPI was an independent predictor for the development of PTDM, together with age, BMI, and HbA1c. Conclusions: Of the pre-transplant factors studied, OGTT 2 h-CPI proved to be an independent predictor of PTDM.