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Oxygen-Detecting Devices Give Misleading Readings In People With Dark Skin

MARY LOUISE KELLY, HOST:

The common fingertip devices that measure oxygen in the blood are increasingly finding their way into people's homes because of the COVID-19 pandemic. These pulse ox devices can sometimes give misleading readings, though, in people with dark skin. That's according to a new study. NPR science correspondent Richard Harris reports.

RICHARD HARRIS, BYLINE: When Detroit's hospitals started to overflow with COVID patients earlier this year, some patients ended up at the University of Michigan in Ann Arbor. And as Dr. Michael Sjoding started treating this influx of largely Black patients, he started noticing something odd about the results from the fingertip device called a pulse oximeter.

MICHAEL SJODING: It spits out this number called an oxygen saturation value, which gives us an understanding of how much oxygen is in the blood.

HARRIS: But that oxygen reading was sometimes off when compared to a more sophisticated test that samples blood from a person's artery. So Sjoding and his colleagues started gathering data, comparing these readings in light-skinned people versus dark-skinned people. They measured how often a pulse ox reading, apparently in the normal range, actually came from someone with low oxygen.

SJODING: We found that this happened much more often in patients that were Black - basically about three times as often.

HARRIS: About 12% of the time, apparently normal readings were actually misleading, Sjoding says.

SJODING: You know, it's not happening a lot. But if you think about how often these measurements are taken, if it's wrong, you know, 12% of the time, I think that - I worry that could be really impactful.

HARRIS: So how aware do you think doctors in critical care and elsewhere in hospitals are? How aware are they of this issue?

SJODING: I don't think they're aware at all. When I ran these analysis, I was just really surprised.

HARRIS: Sjoding says there are a few previous studies about this phenomenon, so specialists in some fields may be familiar with it. He's spreading the word more broadly with a report in the New England Journal of Medicine. He suspects the reason behind this is that the color of light used in pulse oximeters can be absorbed by skin pigment. Dr. Jewel Mullen, associate dean for health equity at the University of Texas Dell Medical School in Austin, agrees this is about skin color, not race. But she's concerned the impact the finding could have on people who may rely on consumer-grade pulse ox devices at home, sometimes in lieu of medical care. Pulse ox devices are still a valuable tool, she says, but it's important to look at the results in context.

JEWEL MULLEN: If somebody has coronavirus and they're feeling really short of breath but they're getting a normal number, say an oxygen saturation of 92 to 96% or more, they should pay more attention to their shortness of breath than what that oxygen is being measured.

HARRIS: Sjoding says these will remain important for hospitals as well. But now he thinks more carefully about how to interpret the readings. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.