Background: The application of GFR estimating equations and classification schema for chronic kidney disease (CKD) has inadvertently led to labeling of some former living kidney donors as having CKD post-donation. GFR equations incorporating CysC and Creat have been recently shown to be more precise in estimating measured GFR (mGFR). We sought to evaluate the performance of those methods in former living kidney donors.

Methods: From a population of 3,698 living kidney donors, 257donors were randomly selected to undergo GFR measurement by iohexol plasma disappearance. Sixty-one % of donors were females, 99.2% were Caucasian. Mean time from donation was 12.2 ± 9.2 years. GFR was estimated using the following models: the Modification of Diet in Renal Disease (MDRD) equation, the Chronic Kidney Disease Epidemiology Collaboration study (CKD-EPI-Creat), and the 2 newly developed formulas using CysC with and without Creat: CKD-EPI-CysC and CKD-EPI-Creat+CysC.

Results: Mean mGFR was 71.8±11.8 mL/min/1.73 m². The MDRD and CKD-EPI-Creat+CysC equations exhibited less bias than the CKD-EPI-Creat and CKD-EPI-CysC equations. Both equations had higher accuracy with 94.2% and 92.6% of estimates falling within 30% of mGFR vs. 87.2% and 85.6% of estimates by CKD-EPI-Creat and CKD-EPI-CysC equations respectively. All 4 formulas demonstrated similar degrees of association with mGFR but CKD-EPI-Creat+CysC showed the highest precision, especially at higher GFR levels (> 60 mL/min/1.73 m²) (R² =0.64).

Conclusion: The newly developed GFR estimation equation incorporating both CysC and Creat is superior compared to other GFR equations, and could be considered as a surrogate for mGFR in situations where more precise GFR estimation is necessary such as post-kidney donation.

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