New Kidney Function Test Takes Race Out of the Equation

By Sue Rochman

nurse prepares man for a blood draw

Researchers have identified an approach to remove race from equations used to estimate a person’s kidney function. These equations have been criticized for potentially perpetuating racial health disparities. The findings, reported Sept. 23 in the New England Journal of Medicine, are expected to inform National Kidney Foundation–American Society of Nephrology Task Force guidelines on evaluating kidney function.

“Our research showed that if you use a blood cystatin C test, instead of a blood creatinine test, you don’t need to include race to get a similarly accurate estimate of kidney function,” said the study’s co-senior author, Alan S. Go, MD, a senior research scientist at the Kaiser Permanente Division of Research in Northern California.

Testing for blood creatinine levels is currently the most commonly used way to measure kidney function. Since the1990s, mathematical equations that include a person’s age, sex, and race along with their creatinine level have been used to determine estimated glomerular filtration rate, known as GFR. Race – classified as Black or non-Black – was added because studies showed that, on average, creatinine levels are higher in people who are self-reported Black versus self-reported non-Black, even when kidney function is the same. Over the past year, the equation’s use of Black race has been used by reporters and activists as a prominent example of possible medical racism.

Cystatin C solves the scientific problem of maintaining comparable accuracy and it achieves the social and scientific goal of getting rid of the need to consider race.

Chi-yuan Hsu, UCSF nephrologist

Cystatin C is a less-widely used test for kidney function. The new study showed that when cystatin C test results were substituted for creatinine test results, race could be taken out of the equation.

“Cystatin C solves the scientific problem of maintaining comparable accuracy and it achieves the social and scientific goal of getting rid of the need to consider race,” said the study’s co-lead author Chi-yuan Hsu, MD, a nephrologist at UC San Francisco and an adjunct investigator with the Kaiser Permanente Division of Research.

Tests for cystatin C are currently available but are not routinely used because they are not fully standardized. They also are significantly more expensive. If cystatin C became more reliable and widely used, the cost of the test would likely come down, the researchers said.

The study also found that race could not be removed from the equation currently used to measure GFR. Drs. Go, Hsu, and their fellow Chronic Renal Insufficiency Cohort Study Investigators showed that independent of age, sex, and measured kidney function, Black race was associated with a 10.7 percent higher serum creatinine level. They also showed that when genetic African ancestry was substituted for race, each 10 percent increase in genetic African ancestry was associated with a 1.3 percent higher creatinine result. In other words, the equation that used creatinine was more accurate if Black race or genetic ancestry was included.

“Our results show that race and genetic ancestry are linked to a person’s creatinine level, and we can’t erase that even if we account for a wide range of other factors, such as muscle mass, dietary protein intake, and other factors that are believed to influence blood creatinine level independent of kidney function,” said Go. “We believe that changing to the cystatin C test will promote more equity for people of all racial and ethnic backgrounds.”

Funding for this study was obtained under a cooperative agreement from the National Institute of Diabetes and Digestive and Kidney Diseases. This work was also supported in part by the University of Pennsylvania; Johns Hopkins University; University of Maryland; Clinical and Translational Science Collaborative of Cleveland; University of Illinois at Chicago; Tulane University; University of California, San Francisco; and the National Center for Advancing Translational Sciences.

Co-authors include Harold I. Feldman, MD, MSCE, Wei Yang, PhD, Debbie L. Cohen, MD, Raymond R. Townsend, MD, and Jianqiao Wang of the University of Pennsylvania, Philadelphia; Rishi V. Parikh, MPH, and Thida C. Tan, MPH, of the Division of Research; Amanda H. Anderson, PhD, Jiang He, MD, PhD, and Katherine T. Mills, PhD, of Tulane University; Teresa K. Chen, MD, MHS, of Johns Hopkins University; Madhumita J. Mohanty, MD, of Wayne State University; James P. Lash, MD, and Milda R. Saunders, MD, MPH, of the University of Illinois-Chicago; Anthony N. Muiru, MD, of the University of California, San Francisco; Afshin Parsa, MD, MPH, of the National Institute of Diabetes and Digestive and Kidney Diseases; Tariq Shafi, MBBS, MHS, of the University of Mississippi Medical Center; Sushrut S. Waikar, of the Boston University School of Medicine; and Myles Wolf, MD, MMSc, of Duke University.

Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America’s leading health care providers and not-for-profit health plans. Founded in 1945, Kaiser Permanente has a mission to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve approximately 12.5 million members in 8 states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal Permanente Medical Group physicians, specialists, and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery, and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education, and the support of community health.  

The University of California, San Francisco (UCSF) is exclusively focused on the health sciences and is dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care. UCSF Health, which serves as UCSF’s primary academic medical center, includes top-ranked specialty hospitals and other clinical programs, and has affiliations throughout the Bay Area.