Undiagnosed diabetes in kidney transplant candidates: a case-finding strategy

Abstract

Background and objectives: Guidelines recommend that candidates for kidney transplantation (KTx) who do not have diabetes perform a pretransplantation oral glucose tolerance test (OGTT) when fasting plasma glucose (FPG) is <110 mg/dl (<6.1 mmol/L); however, the OGTT is potentially costly and cumbersome. We studied the role of the OGTT for diagnosing diabetes and the accuracy of FPG and glycated hemoglobin (HbA(1c)) for predicting a diabetic OGTT before KTx.

Design, setting, participants, & measurements: In this cross-sectional study, 889 first single-kidney transplant candidates without diabetes, mainly white, performed an OGTT during the transplantation workup. Results were studied using receiver operating characteristic analysis.

Results: Of 72 (8.1%) patients with undiagnosed diabetes, only 16 (22%) had a diabetic FPG (> or =126 mg/dl [> or =7.0 mmol/L]). In patients with a nondiabetic FPG, diabetes (2-hour plasma glucose [2h-PG] > or =200 mg/dl [> or =11.1 mmol/L]) was predicted by FPG but not by HbA(1c). Performing the OGTT in patients with FPG 92 to 125 mg/dl (5.1 to 6.9 mmol/L) identified 65 (90%) patients with diabetes (16 by FPG, 49 by 2h-PG) and required seven OGTTs per patient identified. Subjecting all patients with FPG <110 mg/dl (<6.1 mmol/L) to the OGTT identified 60 (83%) patients with diabetes (16 by FPG, 44 by 2h-PG) but required 14 OGTTs per patient.

Conclusions: The OGTT was paramount in finding most cases of undiagnosed diabetes before KTx. FPG but not HbA(1c) predicted a diabetic OGTT. We suggest that white KTx candidates without diabetes perform a pretransplantation OGTT when FPG is 92 to 125 mg/dl (5.1 to 6.9 mmol/L).

Figure 1.

Patient disposition. All adult (≥18 years) patients who had nondiabetic ESRD and were referred for first single KTx within the study period were considered eligible (n = 1111). Upon data retrieval, patients were excluded from participation when they had (1) acknowledged diabetes before transplantation workup or (2) incomplete OGTT data. DM, diabetes mellitus.

Figure 2.

ROC curves. Analyses were performed on patients with FPG <126 mg/dl (<7.0 mmol/L). The ability of FPG (A; AUC 0.734 [95% CI 0.674 to 0.795]) and HbA_1c (B; AUC 578 [95% CI 0.482 to 0.673]) to predict a diabetic 2h-PG (≥200 mg/dl [≥11.1 mmol/L]) parallels the area between the curved and the diagonal reference line (AUC). The top left corner of each panel represents AUC 1.0 (perfect sensitivity and specificity). *Youden index (largest vertical difference between the curve and the reference line); **point closest to the top left corner of the panel.