Performance of the 2021 Race-Free CKD-EPI Creatinine- and Cystatin C-Based Estimated GFR Equations Among Kidney Transplant Recipients

Rationale & Objective: Race-free estimated glomerular filtration rate (eGFR) equations incorporating creatinine with and without cystatin C were recently developed and recommended for routine use. However, the performance of these equations among kidney transplant recipients (KTRs) remains unknown.

Study Design: Cross-sectional study to validate the 2021 race-free Chronic Kidney Disease (CKD) Epidemiology Collaboration (CKD-EPI) eGFR equation based on creatinine alone (eGFR) or based on creatinine and cystatin C (eGFR) among KTRs.

Setting & Participants: KTRs in stable condition (N = 415) from Canada and New Zealand with same-day measurements of creatinine, cystatin C, and glomerular filtration rate (GFR) using radiolabeled diethylenetriaminepentaacetic acid.

Tests Compared: The 2009 CKD-EPI eGFR, 2021 CKD-EPI eGFR, 2012 CKD-EPI eGFR, 2021 CKD-EPI eGFR, 2012 CKD-EPI eGFR, and Modification of Diet in Renal Disease (MDRD) Study eGFR equations were compared with measured GFR.

Outcomes: Bias, precision, accuracy, and correct classification by CKD stage. Bias was defined as the difference between estimated and measured GFR. Precision was represented by the interquartile range. Accuracy was defined as the percentages of participants with eGFRs within 10%/20%/30% (P/P/P) of measured GFR, root mean square error, and mean absolute error.

Results: 87% of patients studied were White, 3% Black, and 10% other races. Mean measured GFR was 53 ± 19 (SD) mL/min/1.73 m. The 2009 and 2021 CKD-EPI eGFR equations demonstrated similar median bias (-2.3 vs -0.2 mL/min/1.73 m, respectively), precision (14.5 vs 14.9 mL/min/1.73 m), and accuracy (P/P/P, 32%/65%/84% vs 33%/63%/84%). The 2012 and 2021 CKD-EPI eGFR equations also demonstrated similar median bias (-3.6 vs 0.3 mL/min/1.73 m, respectively), precision (13.3 vs 14.3 mL/min/1.73 m), and accuracy (P/P/P, 32%/63%/80% vs 32%/67%/83%). No clear difference in performance was detected between the 2021 CKD-EPI eGFR and eGFR equations among KTRs. The proportion of correct classification by CKD stage was similar across all eGFR equations.

Limitations: Moderate sample size, few patients had a GFR <30 mL/min/1.73 m, and the large majority of patients were White.

Conclusions: Among KTRs, the 2021 race-free CKD-EPI eGFR equations perform similarly to the previous CKD-EPI equations that included race correction terms. No significant difference in performance was observed between the 2021 CKD-EPI eGFR and eGFR equations in the kidney transplant population.