New eGFR Formula May Inappropriately Label Black Potential Kidney Donors as Having CKD

A study published in The American Journal of Surgery found that the recent change to remove race from the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula for estimated glomerular filtration rate (eGFR) may incorrectly label potential donors who are Black as having chronic kidney disease (CKD).

The CKD-EPI removed Black race from its equation in 2009, and in 2021, the formula removed the 1159 correction factor that was applied to Black patients that would systemically decrease their eGFR. The researchers hypothesized these changes would lead to more Black patients incorrectly receiving a diagnosis of CKD.

The study used the Scientific Registry of Transplant Recipients data to identify adults who were kidney-only donors from January 1, 2010, through March 3, 2021. All individuals had a predonation eGFR of at least 60 mL/min. Pre-donation Kidney Disease: Improving Global Outcomes CKD G-stage was calculated using eGFR from the 2009 formula and the reclassification of CKD stage in the race-free 2021 formula.

CKD stage from the postdonation follow-up based on the 2009 and 2021 formulas was selected from the higher of the 2 lowest eGFRs. Multiracial donors were excluded from this study.

There were 63,246 donors in the dataset, of which 11.2% were Black and had a mean serum creatinine of 0.88 mg/dL. The eGFR of Black donors was 109.7 mL/min/1.73 m² in the 2009 formula and 97.7 mL/min/1.73 m² in the 2021 formula. Classification of CKD stages was 82.0% vs 65.2% for CKD stage 1, 18.0% vs 34.0% for stage 2, and 0.0% vs 0.9% in stage 3 in Black donors based on 2009 vs 2021 formulas, respectively.

Using the 2021 formula, 17.7% of Black donors had a higher CKD stage prior to donation .

A total of 67.5% of non-Black donors were classified as having CKD stage 1 and 32.5% as having stage 2 disease when using the 2009 formula. These percentages changed to 74.6% and 25.4%, respectively, with the 2021 formula. Seven percent of non-Black donors were reclassified as having a lower stage of CKD.

A total of 9.3% of patients with 2 or more creatinine measurements post donation were Black; mean serum creatinine was 1.24 mg/dL and mean eGFR was 73.2 mL/min using the 2009 formula and 65.6 mL/min/1.73 m² using the 2021 formula. CKD stage classification was 14.2% vs 5.7% for CKD stage 1, 64.2% vs 55.7% for stage 2, and 21.6% vs 38.6% for stage 3 for Black patients in the 2009 and 2021 formulas, respectively. A total of 25.5% of Black donors had a higher classification of CKD stage post donation in the 2021 formula.

In non-Black donors, 7.3% were classified as having CKD stage 1, 56.0% as having stage 2, and 36.7% as having stage 3 disease when using the 2009 formula vs 9.3%, 62.1%, and 28.5%, respectively, with the 2021 formula; 10.1% of non-Black donors were reclassified as having a lower stage of CKD post donation.

Three percent and 1.4% of Black donors younger than 40 years and 40 to 65 years, respectively, would be classified as having CKD via the thresholds for age before donation when using the 2021 formula. Further, 25.3%, 21.5%, and 12.8% of Black donors younger than 40 years, 40 to 65 years, and older than 65 years, respectively, would be classified as having CKD post donation using the eGFR age thresholds from the 2021 formula in donors who would not have CKD in the 2009 formula.

There were some limitations to this study. The retrospective nature limited how to demonstrate causality between the 2021 formula adoption and fewer Black kidney donors and/or adverse outcomes after donation. Data were also lacing about renal parenchymal disease, which limited the ability to accurately diagnose CKD stages 1 and 2.

The researchers concluded that this study proved there are needs for a validated eGFR formula for living kidney donors, GFR measurement rather than estimation, and the education of potential and actual donors for interpretation of CKD staging.

Reference

Orandi BJ, Kumar V, Reed RD, et al. Reclassification of CKD in living kidney donors with the refitted race-free eGFR formula. Am J Surg. Published online September 21, 2022. doi:10.1016/j.amjsurg.2022.09.