October 1, 2020

UW Health, SMPH remove race from kidney function estimation formula and offer alternative

Madison, Wis. — As part of their efforts to address systemic racism in medicine, UW Health and University of Wisconsin School of Medicine and Public Health are calling for an approach to assess kidney function devoid of race.

At issue is how providers estimate kidney function because there is no perfect method for doing so, according to Dr. Arjang Djamali, professor at the UW School of Medicine and Public Health, and UW Health nephrologist.

More than two decades ago, researchers developed a formula that estimates glomerular filtration rate (GFR), a measure of kidney function. The formula is based on a blood test for creatinine, a protein that is released by muscles, and race. The inclusion of race in creatinine-based GFR was based upon observations from several studies that Black participants had higher GFRs when compared to White participants. The researchers suspected that this was due to a higher average muscle mass among Black participants. than the non-Black study participants. In addition, when the formula was first developed the testing sample was composed of primarily non-Hispanic White men.

However, race is a social construct rather than a biological one, and race must not be used as a proxy for muscle mass or kidney function, Djamali said.

Using race in the creatinine-based formula can overestimate GFR, or kidney function, in advanced stages of disease, leading to delays in necessary care and access to kidney transplantation for Black patients.

"Essentially, this calculation would often suggest that a Black patient's kidney function is better than what it really is," Djamali said. "These are the reasons race needs to be eliminated from the formula."

Removing race from the creatinine-based formula could have the unintended consequence to misclassify the stage of kidney disease for about 10% of patients. To help correct this, Djamali and his multidisciplinary team of colleagues propose using a confirmatory cystatin C-based GFR test when accurate kidney disease staging is considered. The cystatin C-based GFR test does not rely on a race-based assumption.

UW Health is beginning to use this test as of today.

"This simple biological test, rather than a social construct, can help eliminate an element of systemic racism in medicine," Djamali said. "We strongly encourage all health systems to follow this example, and for everyone in the practice of medicine to intentionally engage in anti-racism efforts."