Estimating Glomerular Filtration Rate in Kidney Transplantation: Is the New Chronic Kidney Disease Epidemiology Collaboration Equation Any Better?

BACKGROUND: The new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was developed to address the systematic underestimation of the glomerular filtration rate (GFR) by the Modification of Diet in Renal Disease (MDRD) Study equation in patients with a relatively well-preserved kidney function. The performance of the new equation for kidney transplant recipients (KTRs) is unknown. METHODS: We used the plasma clearance of Tc-99m-diethylenetriamine pentaacetic acid to measure the GFR in a cohort of 207 stable KTRs and estimated the GFR with the new CKD-EPI equation. RESULTS: The mean bias for the CKD-EPI equation of -4.5 mL . min(-1) . (1.73 m(2))(-1) was lower than that of the 4-variable MDRD Study equation; however, the 2 equations showed similar variation of individual biases around the mean or median bias, so that only modest improvement was seen in the overall percentage of GFR estimates within 30% of the measured GFR (84% vs 77% for the CKD-EPI vs MDRD Study equations, respectively). In the cohort with a GFR >60 mL . min(-1) . (1.73 m(2))(-1) (n = 98), the CKD-EPI bias was much less than that of the MDRD Study equation [-7.4 mL . min(-1) . (1.73 m(2))(-1) vs -14.3 mL . min(-1) . (1.73 m(2))(-1)], and an accuracy of +/- 30% was seen for 89% of GFR estimates, compared with 77% with the MDRD, Study equation. The variation of the individual biases around the mean bias remained substantial [SD = 13.7 mL . min(-1) . (1.73 m(2))(-1)]. CONCLUSIONS: The CKD-EPI equation shows improved estimation ability, and we recommend that it replace the MDRD Study equation as the currently preferred creatinine-based estimating equation for KTRs. The precision of GFR estimates obtained with the CKD-EPI equation remains suboptimal, however, and we recommend that research on other markers of GFR, such as cystatin C and beta-trace protein, be pursued.