Race-based equations inaccurately estimate the kidney function of Black patients and may delay their kidney transplant eligibility, according to new study findings.¹

Leila R. Zelnick, PhD, of the Kidney Research Institute at the University of Washington in Seattle, Washington, and colleagues compared estimated glomerular filtration rate (GFR) against measured GFR in a subset of patients who self-identified as Black in the Chronic Renal Insufficiency Cohort (CRIC). The investigators found iothalamate-measured GFR (iGFR) of 15 to less than 45 mL/min/1.73 m² in 311 of 1658 Black patients. They calculated individuals’ estimated GFR 3 ways using the widely used creatinine-based Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation – with and without the race coefficient — and the cystatin C-based CKD-EPI equation, which does not include a race adjustment.

Kidney function estimates without the race coefficient corresponded more closely with iGFR, Dr Zelnick’s team reported in JAMA Network Open. The CKD-EPI equation with the race coefficient significantly overestimated iGFR by a mean 3.1 mL/min/1.73 m², whereas the CKD-EPI equation without the race coefficient significantly underestimated iGFR by a smaller margin of −1.7 mL/min/1.73 m². By comparison, the cystatin C-based equation significantly overestimated iGFR by 5.6 mL/min/1.73 m².

Among patients with an iGFR of 20 to 25 mL/min/1.73 m² who were approaching the threshold for kidney transplant eligibility (less than 20 mL/min/1.73 m²), estimated and measured GFR differed by a significant mean 5.1 mL/min/1.73 m² with the race-based CKD-EPI equation compared with 1.3 mL/min/1.73 m² without the race adjustment and with a significant 6.2 mL/min/1.73 m² using the cystatin C-based equation.

Over a median follow-up period of 4 years, calculation of eGFR using the CKD-EPI equation with vs without the race coefficient was significantly associated with a 35% higher likelihood of achieving an estimated GFR of less than 20 mL/min/1.73 m² and a shorter median time to kidney transplant eligibility of 1.9 years, the investigtors reported. The cystatin C-based equation performed no better than the standard race-based equation in this scenario.

Another recent analysis, which included 2225 Black patients, found that 3.1% of patients overall would be reassigned from an estimated GFR greater than 20 mL/min/1.73 m² to an estimated GFR less than 20 mL/min/1.73 m² with removal of the race coefficient. In that study, which was published in the Journal of General Internal Medicine², none of the 64 Black patients who met those criteria were currently referred, evaluated, or waitlisted for a kidney transplant. Other research has shown that Black patients are less likely to be referred for transplantation, less likely to be waitlisted, and less likely to receive a transplant for various reasons.

According to an editorial accompanying the study by Dr Zelnick and colleagues, the latest findings provide evidence to support universal removal of the Black race coefficient in kidney function estimating equations.³

“Use of racialized eGFR equations may not only produce biased kidney function estimates, but it may also reinforce the effects of structural racism on Black individuals by systematically and differentially influencing physicians’ clinical decisions and practice patterns,” L. Ebony Boulware, MD, MPH, of Duke University School of Medicine in Durham, North Carolina, and coauthors commented. The editorialists advocated for efforts toward “precise and individualized” measures of kidney function to guide kidney care.

In August 2020, a joint American Society of Nephrology (ASN)-National Kidney Foundation (NKF) task force was created to reassess the use of race in diagnosing kidney disease, as a growing number of institutions around the United States eliminate race in kidney function estimates.⁴ This task force is currently soliciting input from health professionals, scientists, patients, and other stakeholders and will present a final report this spring.

“The task force has been receiving expert testimony and assessing the scientific literature… It is now deliberating to meet its charge to ensure that GFR estimation equations provide an unbiased assessment of kidney function,” Tod Ibrahim, ASN executive vice president commented in Kidney News, an ASN publication.⁵ “ASN and NKF are committed to reversing the racial health inequities in the United States through efforts that address both health disparities and social determinants of health.”

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