A new study claims that one million Black adults in the United States could be treated earlier for kidney disease if doctors were to remove a controversial ‘race-based correction factor’ from an algorithm they use to diagnose people and decide whether to administer medication.

Critics of the factor question its medical validity and say it potentially perpetuates racial bias — and that the latest study, published in Jama, strengthens growing calls to discontinue its use.

“A population that is marginalized and much less likely to have necessary resources and support is the last group we want to put in a situation where they’re going to have delays in diagnosis and treatment,” says nephrologist Keith Norris at the University of California, Los Angeles, who argues for retiring the correction until there’s clear evidence that it’s necessary.

Others claim that the correction is based on scientific data that can’t be ignored, although they, too, agree that its basis on race is a problem.

According to the College of American Pathologists in Northfield, Illinois, variations of race-corrected eGFR algorithms are now used in more than 90% of pathology labs across the United States. In the past few years, institutions including Beth Israel Deaconess Medical Center in Boston, Massachusetts, have dropped the correction factor. None of them has yet released data on the action’s impact.

In the latest analysis, researchers aimed to assess what would happen if they removed the race-based correction factor for a representative group of people. The team examined the medical records of 9,522 Black people included in the National Health and Nutrition Examination Survey, a programme run by the US Centers for Disease Control and Prevention that maintains a national database of health statistics.

Although it was unsurprising that dropping the correction would increase the number of Black people diagnosed with kidney disease, “the size of the effect surprised us”, says Arjun Manrai, a computational health researcher at Harvard Medical School in Boston, who led the study. Removing it would lead to a change in diagnosis for 3.5% of Black adults from ‘disease free’ to having early-stage kidney disease (extended to the US population, this would be one million Black adults).

Removing it would also shift the status of 29% of Black patients from having early-stage to advanced disease. Getting rid of the correction, says Manrai, could drastically alter these people’s access to medications for common conditions such as hypertension or diabetes, because the drugs can have side effects on the kidneys. Overall, it would also increase the number of Black people with kidney disease who are eligible to receive a transplant.

Read the full research paper here