Pulse oximeters are notoriously inaccurate for darker skin tones—and that may have led to COVID treatment delays, study finds

Racial biases abound in the U.S. healthcare system, as evidenced by the lower standard of care often available in predominantly nonwhite communities, higher-than-average mortality and morbidity rates among the Black population and diagnostic and device standards that either cater only to white patients or make faulty race-based calculations.

Straddling several of those categories are repeated findings that pulse oximeters are among the medical technologies that are less effective in patients with darker skin tones—combined with a new study indicating that that disparity may have led to delays in crucial COVID-19 treatment.

Pulse oximeters send beams of light through the skin to measure the oxygen saturation level of the blood. Because many of the devices were developed using mostly white test subjects, research has found that they’re often less accurate when measuring blood oxygen levels in people with darker skin. One study published last year, for example, found that hypoxia—in which low blood oxygen levels lead to low levels of oxygen in the tissues—went undetected by pulse oximetry nearly three times more often in Black patients than in white patients.

The new study, published this week in the journal JAMA Internal Medicine, began by looking retrospectively at blood oxygen saturation readings captured by both pulse oximetry and arterial blood gas in more than 7,100 COVID patients.

That analysis confirmed previous findings, with the researchers concluding that “pulse oximetry overestimated arterial oxygen saturation among Asian, Black and Hispanic patients compared with white patients.” Specifically, they found that about one-third of each of the Asian, Black and Hispanic patients had at least one unidentified case of hypoxia, compared to less than 20% of the white patients.

In a separate retrospective analysis, the research team identified nearly 2,000 Black and Hispanic patients from a pool of more than 6,600 COVID patients. Based on additional health data, they predicted that pulse oximetry had likely overestimated the oxygen saturation levels in the selected group, which in turn led to a “statistically significant delay” in when they received needed COVID treatments—since therapies like supplemental oxygen don’t begin until oxygen saturation dips to a certain level.

In conclusion, the researchers wrote in the study, “This disparity may contribute to worse outcomes among Black and Hispanic patients with COVID-19.”

Despite those disheartening results, there is a light at the end of the tunnel. Several devicemakers are developing pulse oximeters that are designed to take accurate readings for people of all skin colors. In late 2020, Atlanta-based Safe Heart landed FDA clearance for its iOximeter, which it says delivers highly accurate readings not impacted by skin tone.

And earlier this year, a Ph.D. student at Brown University presented early results for a device that takes a new approach to pulse oximetry, emitting radially polarized light that avoids being absorbed by melanin in the skin—the underlying cause of inaccuracies in pulse oximetry readings.