For years, Black people have waited longer for kidney transplants because of their race. A new rule aims to fix that.

Katherine Anderson’s kidneys have been going downhill for years, increasingly unable to filter her body’s waste products from her blood. She is often exhausted and has no appetite, losing 20 pounds in the last year alone from her slender, 5-foot-5½ frame.

On Jan. 27, she finally got good news: Thomas Jefferson University Hospital placed her on the waiting list for a kidney transplant.

But two months later, the 59-year-old Norristown woman, who is Black, got a follow-up message that left her confused. It said that, in the past, doctors had estimated her kidney function with a formula that included race as a variable, making her and other Black patients appear healthier than they really were. When the hospital used a newer, race-neutral formula to recalculate Anderson’s kidney function, it found that in fact, she should have been added to the transplant waitlist more than five years ago.

Hospitals nationwide have sent similar letters to more than 3,700 Black people with kidney disease, in response to a new federal requirement that patients’ kidney function be estimated without taking their race into account. Thousands more are expected to receive such letters by year’s end, as hospitals go through their waitlists to determine who should get additional credit to shorten their wait for a life-saving transplant.

The backstory of why race was included in the older formulas is complicated. The short version: The formulas were developed in a quest for more accuracy, and for many patients, they represented an improvement over inexact estimates of kidney function that had been used before. But in recent years, reviewers have determined that the evidence for treating Black patients differently was flawed and incomplete, rooted in medical racism.

When using the older formulas, doctors had overestimated the kidney function of some Black patients by as much as 20%. In some cases, that meant they waited years longer than non-Black patients to get a new kidney, if they got one at all. Every year, thousands of people in the United States die while waiting for a transplant.

Jefferson is a leader among transplant centers in using a newer, race-neutral formula to update its kidney waitlist. As of April 10, the hospital had credited 102 Black patients with additional waitlist time, representing one-eighth of patients nationwide who’d had their waitlist time augmented by that date.

Since then, the transplant staff has done it for 70 more, coming in on weekends to pore over old lab results and rerun the numbers. The result: On average, the 172 patients have qualified for an additional two years of credit for waitlist time, transplant surgeon Jaime Glorioso said. Seven already have undergone transplants.

“This adjustment is correcting for inequity,” she said. “These are peoples’ lives.”

For Anderson, the recalculation meant she should have gone on the waitlist in December 2017. A few days after she got the notice, a staff member from the Jefferson Transplant Institute followed up with a phone call, explaining that it was positive news.

But Anderson’s reaction was mixed.

“I had more questions than anything,” she said. “Like, how could this happen?”

Kidney disease can develop gradually over years, and it is helpful to catch it in the early stages, when many patients have no symptoms. But it takes at least four hours for a precise measurement of how well the bean-shaped organs are filtering the blood — an impractical timeframe for widespread screening.

So, instead, physicians make indirect estimates, using various formulas based on the amount of a substance called creatinine in the person’s blood. (Higher creatinine levels, generally speaking, can mean the kidneys are not filtering as well as they should.)

One such formula, developed in a 1999 study, became widely accepted in the field because it was more accurate than others. That is, the creatinine-based formula provided an estimate of kidney function that was reasonably close to the direct measurements that took hours.

But there was a new wrinkle: Unlike the earlier formulas, the new one included race as a variable.

That’s because in the study, for a given level of kidney function, Black people had higher creatinine levels than non-Black patients, on average. In order to plug Black patients’ creatinine levels in a formula, the researchers determined that they needed to use a “multiplication factor.” Black patients’ estimated kidney function, they calculated, should be adjusted upward by 18%.

Few doctors, if any, raised concerns about the formula. And as newer calculations were developed, most followed the 1999 example, including race as a variable.

But Toni Martin, a primary-care physician in Berkeley, Calif., was at a loss.

Time after time, her Black patients asked her why their estimated kidney function had been adjusted upward. Why, for a given creatinine level in the blood, were they deemed to have healthier kidneys than their white counterparts, meaning they would have to wait longer for a transplant?

She did some research, looking up the original 1999 study, and the answer troubled her. The study’s authors had concluded that Black people likely had higher creatinine levels because they had more muscle mass.

To Martin, who is Black, that sounded like bad science from an earlier, racist era — when Black people were thought to be poor swimmers because of denser bones, or were judged to be “inferior” due to measurements of the skull.

Though not a kidney specialist, Martin called the editor of the American Journal of Kidney Diseases in 2011 and proposed writing an essay about why the formulas were off-base. In the result, titled The Color of Kidneys, she made her case:

The so-called races are not distinct biological categories, but labels drawn from the superficial characteristics of hair and skin color. Yes, some characteristics may be slightly different from race to race, on average, but generally the average differences between two racial groups are smaller than the differences within a group. In other words, although some Black people may have higher creatinine levels than white people, plenty do not. There is no scientific basis for slotting everyone into a racial box, she wrote.

And even if there were, who decides on the label? The patient? The doctor? What about people with ancestry from multiple races?

“I suspect that few clinicians could guess President Obama’s ancestry by looking at him,” she wrote. “And if they could, which [number] should they use?”

Little by little, others started to listen. And in 2021, a national team of kidney specialists came up with a new, race-neutral formula.

One of the authors was Andrew Levey, a Tufts Medical Center kidney specialist who was part of the team that came up with the original, race-based formula in 1999.

He now thinks the old formula that he helped develop, though more accurate than earlier formulas, was a mistake. In an interview, he cited some of the same reasons as Martin. Race is not a biological category, he said, but a social construct.

“It turned out that the extra accuracy that we were able to obtain from including race in the prediction was not worth the tremendous objection to using a social construct,” he said.

Among those joining him in crafting a new, race-neutral formula was Nwamaka Eneanya, an adjunct faculty member at the University of Pennsylvania’s Perelman School of Medicine.

The new formula is not perfect, either, but it does not systematically disadvantage one racial group over another, she said.

“The old formulas were flawed from the outset,” she said. “You can’t continue to use something like that.”

By the end of this year, hospitals are required to go through their lists and recalculate the kidney function of all Black patients using a race-neutral formula — either the new one developed by Levey, Eneanya and their colleagues, or one of several other options.

Some hospitals are moving faster than others.

As of June 5, just 76 of the nation’s 200-plus transplant centers had submitted waitlist adjustments to UNOS, the not-for-profit organization that manages the U.S. transplant network. A total of 3,788 patients so far have been credited with additional wait time, including the 172 at Jefferson, 125 at Temple University Hospital, and 40 at Penn Medicine.

Anderson, the Norristown woman now on Jefferson’s waiting list, is happy that she is in line for a new organ.

But her feelings are bittersweet, as she is not the first family member with kidney trouble.

Anderson was just 10 years old when her mother was diagnosed with kidney disease, in the early 1970s. Her mother was so sick that family members told her she would have to help take care of her younger siblings, she recalled.

Yet, despite her illness, her mother did not get a transplant until 1999. She died of other causes in 2022, but her ongoing struggle with kidney disease made her life a challenge.

Anderson now wonders: Had her mom’s kidney function been evaluated with the new, race-neutral formula, might she have gotten a kidney sooner? Might she even be alive today?

Two of her sisters also have kidney disease, one of whom got a transplant in 2005. Did she, too, wait longer than she had to?

“How many people of color died waiting on a kidney because of this error?” Anderson asked. “My heart is heavy because of this.”

Now that she’s on the list, Anderson has no way of knowing when a compatible donor kidney from the greater Philadelphia area will become available.

All she knows is that, on average, patients spend four years on the list before receiving a transplant. And she has now been credited for waiting more than five.