How an Algorithm Blocked Kidney Transplants to Black Patients

Black people in the US suffer more from chronic diseases and receive inferior health care relative to white people. Racially skewed math can make the problem worse.

Doctors often make life-changing decisions about patient care based on algorithms that interpret test results or weight risks, like whether to perform a particular procedure. Some of those formulas factor in a person’s race, meaning patients’ skin color can affect access to care.

A new study of patients in the Boston area is one of the first to document the harm that can cause. It examined the effect on care of a widely used but controversial formula for estimating kidney function that by design assigns Black people healthier scores.

The study analyzed health records for 57,000 people with chronic kidney disease from the Mass General Brigham health system that includes Harvard teaching hospitals Massachusetts General and Brigham and Women’s. One third of Black patients, more than 700 people, would have been placed into a more severe category of kidney disease if their kidney function had been estimated using the same formula as for white patients.

That could have affected decisions such as when to refer someone to a kidney specialist, or refer them for a kidney transplant. In 64 cases, patients’ recalculated scores would have qualified them for a kidney transplant wait list. None had been referred or evaluated for transplant, suggesting that doctors did not question the race-based recommendations.

“That was really staggering,” says Mallika Mendu, an assistant professor at Harvard Medical School and kidney specialist at Brigham and Women’s whose work on the study convinced her to stop using the race-based calculation with her own patients. “We know there are already other disparities in access to care and management of the condition. This is not helping.”

The study is the most recent of several signs that math tools exacerbate health inequalities. Last year, software used by many health systems to prioritize access to special care for chronic conditions was found to systematically privilege white patients over Black patients. It didn’t explicitly take account of race, but replicated patterns in access to health care caused by factors like poverty.

The kidney algorithm, by contrast, is one of many clinical decision algorithms that explicitly take account of race. A recent review listed more than a dozen such tools, in areas including cancer and lung care. In August, a group of Black retired NFL players sued the league, claiming it used an algorithm that assumes white people have higher cognitive function to decide compensation for brain injuries.

The issue is winning more attention, including from federal lawmakers. Representative Richard Neal (D-Massachusetts), chair of the House Ways and Means Committee, says the kidney study underlines the need to reconsider use of race in all medical algorithms. “Many clinical algorithms can result in delayed or inaccurate diagnoses for Black and Latinx patients, leading to lower-quality care and worse health outcomes,” he says.

Neal has asked medical societies and the Centers for Medicare & Medicaid Services to investigate the impact on patients of clinical algorithms that use race. Last month, Senator Elizabeth Warren (D-Massachusetts) and others asked the Department of Health and Human Services to investigate race-based medical algorithms.