Omitting Race from Kidney Function Equations Leads to More Accurate Results

At the end of September, a paper appeared in the New England Journal of Medicine that showed omitting race from equations for estimated glomerular filtration rate (eGFR) leads to more accurate results when determining kidney function.

The researchers, led by Lesley Inker, MD, MS, director of the Kidney Function and Evaluation Center at Tufts Medical Center in Boston, Massachusetts, point out that the current equations that use creatinine or cystatin C incorporate age, sex, and race to estimate kidney function, but the authors write that race in these equations is a social construct and not a biological one. “Inclusion of race in GFR estimating equations, along with other algorithms in medicine, is facing increasing scrutiny because race is a social and not a biologic construct; its inclusion ignores diversity within and among racial groups and may contribute to systemic racism in medicine,” the authors write.

For this study, the researchers developed three new eGFR equations without using race from two development data sets – 10 studies for serum creatinine and 13 studies for both serum creatinine and cystatin C – as well as a validation set of 12 studies. About 14% of participants in the validation set were Black, and the researchers found that the current creatinine equation that incorporates race overestimated GFR in Black patients. “When the adjustment for Black race was omitted from the current eGFR equation, measured GFR in Blacks was underestimated,” the authors write.

The researchers’ new equation using age and sex but not race underestimated GFR in Black participants and overestimated GFR in non-black participants. New creatinine–cystatin C equations without race were more accurate than new creatinine equations, with smaller differences between race groups, the authors write. “New eGFR equations that incorporate creatinine and cystatin C but omit race are more accurate and led to smaller differences between Black participants and non-Black participants than new equations without race with either creatinine or cystatin C alone,” they conclude.

The same day the NEJM paper was published, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Diseases released its final report, which outlines a new race-free approach to diagnose kidney disease. In the report, the NKF-ASN Task Force recommends the adoption of the new eGFR 2021 CKD EPI creatinine equation that estimates kidney function without a race variable. The task force also recommended increased use of cystatin C combined with serum (blood) creatinine, as a confirmatory assessment of GFR or kidney function.

“I am honored to have been a part of the NKF-ASN Task Force. By careful review of the evidence and perspectives shared with us, and listening and learning from each other, we were able to arrive at a recommendation for estimating GFR that does not include race that is based on rigorous science, patient centered, and can be immediately implemented across all clinical laboratories,” Inker says. “We hope that our emphasis on an overall approach to assess kidney function using initial tests followed by more accurate tests as the clinical situation requires, will increase awareness of the importance of careful consideration of GFR in all patients.”

“We appreciate the patience of the community as the Task Force developed a sound strategy to not disproportionately disadvantage patients from any particular racial or ethnic group.  Our approach was guided by health equity, patient centeredness and patient safety, and was informed by evidence,” adds Neil Powe, MD, MPH, MBA, FASN chief of Medicine at the Priscilla Chan and Mark Zuckerberg San Francisco General Hospital and the Constance B. Wofsy Distinguished Professor, Vice-Chair of Medicine at the University of California San Francisco and co-chair of the joint NKF-ASN task force. “We hope strong efforts will develop new, more informative, GFR markers and unite all of us in a focus on interventions to eliminate health disparities, thereby improving the quality of care for everyone in the United States.”

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