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Fixing Racial Bias in a Key Covid Diagnostic Tool

Researchers say pulse oximeters don’t accurately detect oxygen levels for people with darker skin. The search is on for better options.

Skin tone, skin texture, and even nail polish can affect absorption.

Skin tone, skin texture, and even nail polish can affect absorption.

Photographer: Grace Cary/Bloomberg

Early in the pandemic, emergency room doctors had to quickly decide whom to hospitalize and whom to send home. One handy tool for making those decisions was the pulse oximeter—a matchbox-sized device that clips onto a finger and measures oxygen levels, a key metric for understanding the severity of a patient’s illness. The problem was, the method didn’t really work on people of color. “I was taking care of an African American woman with asthma and Covid,” says Ashraf Fawzy, a critical care doctor in Baltimore. “We were turning down her oxygen because the pulse oximeter was telling us the levels were adequate, but she was complaining of shortness of breath.”

Fawzy and Tianshi David Wu, an intensive care doctor in Houston, examined the issue by comparing pulse oximeter readings to blood test results. They found huge discrepancies between the two methods that contributed to a lack of recognition of severe Covid, delaying treatment for Black and Hispanic patients. Their findings, reported in JAMA Internal Medicine, echoed a study published two years ago by the New England Journal of Medicine showing that Black patients were almost three times more likely than Whites to have low oxygen levels that went undetected by a pulse oximeter. “The degree of bias is worse the lower the true oxygen number is,” Wu says.