Criteria for Prediabetes and Posttransplant Diabetes Mellitus after Kidney Transplantation: A 2-Year Diagnostic Accuracy Study of Participants from a Randomized Controlled Trial

Posttransplant diabetes mellitus (PTDM) and prediabetes (impaired glucose tolerance [IGT] and impaired fasting glucose [IFG]) are associated with cardiovascular events. We assessed the diagnostic performance of fasting plasma glucose (FPG) and HbA(1c) as alternatives to oral glucose tolerance test (OGTT)-derived 2-hour plasma glucose (2hPG) using sensitivity and specificity in 263 kidney transplant recipients (KTRs) from a clinical trial. Between visits at 6, 12, and 24 months after transplantation, 28%-31% of patients switched glycemic category (normal glucose tolerance [NGT], IGT/IFG, PTDM). Correlations of FPG and HbA(1c) against 2hPG were lower at 6 months (r = 0.59 [FPG against 2hPG]; r = 0.45 [HbA(1c) against 2hPG]) vs. 24 months (r = 0.73 [FPG against 2hPG]; r = 0.74 [HbA(1c) against 2hPG]). Up to 69% of 2hPG-defined PTDM cases were missed by conventional HbA(1c) and FPG thresholds. For prediabetes, concordance of FPG and HbA(1c) with 2hPG ranged from 6%-9%. In conclusion, in our well-defined randomized trial cohort, one-third of KTRs switched glycemic category over 2 years and although the correlations of FPG and HbA(1c) with 2hPG improved with time, their diagnostic concordance was poor for PTDM and, especially, prediabetes. Considering posttransplant metabolic instability, FPG's and HbA(1c)'s diagnostic performance, the OGTT remains indispensable to diagnose PTDM and prediabetes after kidney transplantation.