Pulse Oximeters Can Give Inaccurate Results to People With Dark Skin, a Study Found

A device that measures blood oxygen levels may not work as well depending on the color of your skin.

If you have a heart or lung condition, you might be familiar with a pulse oximeter—a small, rectangular device that clips onto your finger and reads your blood oxygen and heart rate. During the COVID-19 pandemic, many people have invested in an oximeter, because abnormal blood oxygen or heart rate could possibly signal a respiratory issue that might be linked to the coronavirus. But a pulse oximeter may not suitable for everybody, according to a report published in The New England Journal of Medicine.

Discovering the Problem

Researchers from the University of Michigan hospital in Ann Arbor found that the device can sometimes give misleading results in people with dark skin. They became aware of this when they received an influx of COVID-19 patients from Detroit's overcrowded hospitals, many of whom are Black. Lead author Michael W. Sjoding, MD, noticed that there was something strange about hospitals' oximeter results. The oximeter reading was sometimes off when it was compared with a more advanced test that samples blood from an artery.

"We found that this extremely common medical device has a meaningful difference in accuracy in patients who described themselves as Black compared to those who described themselves as White," Dr. Sjoding, who specializes in pulmonary diseases, internal medicine, and critical care medicine, tells Health. Specifically, the study found that Black patients were more than three times as likely as White patients to have a pulse oximeter reading in the normal range yet a low reading once they were given the more sophisticated artery test.

What Is a Normal Blood Oxygen Level?

A normal blood oxygen saturation level is 94 to 100 percent, critical care pulmonology expert Vandana A. Patel, MD, a clinical advisor for the online pharmacy Cabinet, previously told Health. If a patient gets a result lower than 90 percent, they might experience confusion and lethargy because the brain isn't getting enough oxygen. If the oxygen saturation level drops to the low 80s, there's a risk of organ damage or even death.

Dr. Sjoding was surprised by his findings, which were the result of looking at data from approximately 10,000 patients. "The oximeter is a device I use all the time to make decisions about how to care for patients," he says. "I use it more often than a thermometer, for example. So the fact that these devices have any bias at all was just really surprising."

What's Causing the Discrepancy?

Further investigations are required, but Dr. Sjoding suspects that the reason for the discrepancy is that the color of light used in the pulse oximeter can be absorbed by skin pigment—and pigment grains are larger and more abundant in darker skin.

"We need to be more careful about how we care for people with darkly pigmented skin," Dr. Sjoding says. "We have to remain diligent. We can't be completely reassured by the fact that their pulse oximeter is reading in the low normal range but they are saying that they feel really sick."

This is an important point for anybody who uses a pulse oximeter. If you have COVID-19 and you experience breathlessness, yet your pulse oximeter tells you that your oxygen saturation is within a normal range, you should still seek medical attention. "You shouldn't ignore those feelings just because the number seems to say you're still ok," Dr. Sjoding explains.

You should also check in with your doctor if your reading drops significantly, even if it's still within the normal range. And if you feel poorly and the saturation is reading low, you definitely shouldn't ignore it. "You need to be seen by a doctor immediately," Dr. Sjoding says.

An oximeter at home can still be valuable, Dr. Sjoding points out. "It's still really important technology, and is absolutely worth using," he says. "Our study is really focused on the situation where the reading is in the normal range, to help people understand its limitations. This could have important implications for how we care for patients with COVID-19 and far beyond."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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