Cystatin C–Based Equation for Predicting the Glomerular Filtration Rate in Kidney Transplant Recipients

Abstract Background Precise monitoring of the glomerular filtration rate (GFR) is needed to estimate the allograft function in kidney transplant recipients (KTRs). The GFR is widely estimated with the use of formulas based on serum cystatin C (SCys) and serum creatinine (SCr) levels. We compared the efficacy of SCys-based equations with that of SCr-based equations to predict the allograft function. Methods We calculated the Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI Cr), CKD-EPI creatinine–cystatin C (CKD-EPI Cr/Cys), and CKD-EPI cystatin C (CKD-EP ICys) equations in 70 KTRs. The measured GFR (mGFR) was defined as the GFR estimated by technetium-99m–diethylene triamine pentaacetic acid ( 99m Tc-DTPA) clearance. The accuracy and precision of the equations were compared with the mGFR. The performance characteristics of SCr and SCys were analyzed with the use of receiver operating characteristic (ROC) curves to ascertain the sensitivity and specificity at the cutoff value of  2 DTPA. Results Overall, MDRD and CKD-EPICys did not show significant differences from mGFR ( P  = .05 and P  = .077, respectively), whereas CKD-EPI Cr and CKD-EPI Cr/Cys significantly underestimated mGFR ( P P  = .005, respectively). In the subgroup of patients with mGFR  2 , CKD-EPI Cys showed little bias ( P  = .122), whereas MDRD significantly underestimated mGFR ( P  = .037). The area under the ROC curve for predicting mGFR  2 was 0.80 for SCys, which was better than that for SCr at 0.763. Conclusions Cystatin C–based equations showed better predictive performance of the allograft function than creatinine-based equations for the KTRs, including patients with lower GFR. Cystatin C level might be a good alternate measurement to monitor the allograft function.