Taking Racism out of the Kidney Disease Equation

The first sign something was wrong with Curtis Warfield came in 2005, when a lab test found protein in his urine during a routine checkup. In 2012, Warfield was diagnosed with stage 3 kidney disease. Two years later, he started dialysis.

“When you get diagnosed, you’re sitting there kind of like a deer in headlights. You don’t know what’s going on. You don’t know what’s coming next,” Warfield said. “All you know, you have this disease.”

Warfield, a Black man, was 52 years old, had been healthy, and had no family history of kidney disease. As his condition worsened and he worked his way through treatment options, he experienced a form of racism without knowing it: a math equation that counted his race when it estimated his kidney function.

That equation, called the estimated glomerular filtration rate or eGFR, is an important variable that helps dictate the course of treatment for an estimated 37 million people with kidney disease across the country. The eGFR equation estimates how well a person’s kidneys are filtering blood, taking into account a person’s age, gender, and levels of creatinine, a waste product naturally made by people’s bodies that is cleared out through the kidneys. But it has long involved a controversial variable: race.

If a person self-identifies as Black, the equation adjusts their score, increasing it. No other races are counted in the equation. As a result, Black people have higher eGFR scores than people of other races. Those scores, which estimate how well kidneys are functioning, influence doctors’ treatment recommendations. The lower the score, the more likely a patient is to begin dialysis or even to receive a kidney transplant. 

As the disparities facing Black people with kidney disease became more widely studied, the race-based eGFR has been increasingly challenged by nephrologists, high-profile kidney disease organizations, and, crucially, medical students who questioned their educators about the biological basis for differentiating between Black and non-Black people.

Warfield has been advocating for other people with kidney disease since he received a transplant in 2015. He joined a multi-organization task force spearheaded by the National Kidney Foundation in 2020. The task force spent months diving into the issue, challenging the inclusion of race in the eGFR, and ultimately initiated two new equations for estimating kidney function.

The new, race-neutral equations came out this past fall. And in February, the United Network for Organ Sharing (UNOS), the nonprofit organization that manages the organ donation and transplant system in the U.S., proposed dropping the use of the racialized eGFR in favor of a race-neutral eGFR. As a result, kidney care in the U.S. is at a watershed moment of moving past a deeply entrenched, institutionally racist equation.

Dropping the race factor from kidney estimations is a crucial step in reducing disparities in kidney disease and treatment, according to specialists on the National Kidney Foundation’s task force. Black Americans are at a disproportionate risk for conditions that contribute to kidney disease, like high blood pressure, diabetes, and heart disease. While Black people make up less than 14% of the population in the U.S., they encompass 35% of people on dialysis, according to the National Kidney Foundation.

“People that are Black are much less likely to be referred to transplant even when they are on dialysis. When referred, they’re much less likely to be listed. When listed, they’re much less likely to be given a kidney transplant. There are disparities every step of the way,” said Rajnish Mehrotra, MD, chief of nephrology at Harborview Medical Center and a University of Washington professor of nephrology and medicine.

Those disparities were the basis of increased questions from medical students over the past several years, Mehrotra said, particularly when it came to the equation the students were learning to assess kidney function.

“They were told in the class that there’s an equation in which it reports a different number if you’re Black versus if you’re not Black. And they challenged the premise of that, as in like, ‘What is the evidence that there is a difference there?’’ Mehrotra said. “And so the deeper we dug in terms of searching for the evidence to support a differentiated reporting by race, we came to the assessment that the evidence supporting that is not strong at all.”

University of Washington Medicine, where Mehrotra works, became one of the first institutions to do away with the race variable of the eGFR equation back in June 2020.

But there was a broader movement going on as well, involving the premier professional societies for kidney specialists, the National Kidney Foundation and the American Society of Nephrology, as well as patient advocates (including Warfield), clinicians, scientists, and laboratory technicians, all convening with the goal of phasing out the racialized eGFR in favor of a race-neutral approach.

In June 2021, a year after Washington Medicine dropped the racialized eGFR, the task force formed by those organizations released an interim report questioning the use of race as a factor in diagnosing kidney care.

The race variable in the eGFR had come about based on research from the 1990s, according to the report. Published in 1999, the Modification of Diet in Renal Disease (MDRD) study was one of the first to include Black people – an earlier kidney function estimation equation was based entirely on white, male patients’ information – and it found higher levels of serum creatinine among Black adults than their white counterparts, the task force authors write in their report.

At the time of the MDRD, making a mathematical adjustment based on race was seen as an advance because including Black people in studies at all was an advance, according to the report.

But within the MDRD is a troubling justification for higher creatinine levels among Black people: earlier studies had shown that “on average, black persons have greater muscle mass than white persons.” The three studies cited there, published in 1977, 1978 and 1990, compared different health measures, including serum creatinine kinase and total-body potassium levels, in Black and white study participants. The studies all state that separate reference standards are needed for Black people, attributing differences in results to differences in racial biology.

Today, those conclusions would be challenged.

“Our understanding of race has evolved over the last quarter century,” said Paul Palevsky, MD, the president of the National Kidney Foundation and a professor at the University of Pittsburgh, one of the primary organizations in the task force. “Rather than being biologically based, race is much more of a social construct than anything else.”

In September 2021, the task force released their two new equations that estimate kidney function. Neither uses race as a factor. One is very similar to the racialized eGFR, which measures creatinine. The other equation adds a second test that measures cystatin C, another chemical in the blood that serves as a filtration marker.

Both equations have been recommended because even though creatinine testing is available at virtually all laboratories across the country, cystatin C is not, leading to a higher price tag and decreased access to the test. The process to move laboratory practices toward the new standard is underway, said Palevsky, and he’s hopeful that the major labs will make the change over the next several months.

“In medicine, the time that it normally takes from when a clinical practice guideline or recommendation is published to when it really seems to enter into clinical care is about a decade,” Palevsky said. “In this case, what we’re seeing is a very rapid implementation of the new equation.”

The new equations are slightly less precise compared with the old equation, Palevsky and Mehrotra agree. But the estimates are just that – estimates – and should be used as just one part of a much more comprehensive clinical analysis of a person’s health and needs.

And as racial disparities across medicine continue to be studied and understood, the impacts of factoring in race in health care decisions can have a corrosive effect beyond an individual person and their diagnosis, Palevksy said. “As we teach medical students and residents, if we use race-based algorithms, we are reinforcing for them this concept, this false concept, that race is a biological determinant of disease, which it is not,” Palevsky said.

Systemic racism factors into Black people’s health outcomes in many different ways, from chronic stress of experiencing racism to limited access to healthy food to bias of health care providers. These problems are deeply entrenched and require their own sustained solutions.

The new eGFR equation, though, is a step in the right direction, Palevsky said.

“Will it solve the problem of disparities in kidney care? I think we would be deluding ourselves to think that a simple change in an equation is going to solve much, much deeper-rooted problems,” Palevsky said. “Certainly just changing an equation isn’t going to solve the problems of disparities, many of which are rooted in historic racism.”

Those disparities will only be meaningfully lessened by large-scale investment into the health of poor communities. But the eGFR equation is a meaningful step for Black people with kidney disease, nonetheless. The benefits of the new eGFR equation, Warfield said, expand beyond the equation itself.

“It’s opening eyes and doors to other disparities that are going on, at least within the kidney community, and getting people to talk about and look at what all is going on,” Warfield said. “It’s good to have to know that the patient’s voice is now sitting at the table and being listened to, and not just decided by the medical community.”

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