A new multicenter study raises the question of whether reliance on pulse oximetry as an indication of oxygen status contributes to poorer outcomes in people of color. Previous studies have suggested that at lower oxygen saturation levels, pulse oximeter readings may overestimate the amount of oxygen in the bloodstream of patients with dark skin. Researchers have noted that while the U.S. Food and Drug Administration (FDA) requires demographic subgroup data in device applications, most calibration and confirmation tests of pulse oximeters have been done on people with light skin. Acknowledging possible misreads, in February the FDA issued a warning citing "multiple factors" that can affect pulse oximetry accuracy, including "poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and use of fingernail polish."

The new research looked at adult inpatients on supplemental oxygen at the University of Michigan Hospital from January through July 2020, and at ICU patients in 178 hospitals from 2014 through 2015. Pulse oximetry measures were paired with arterial blood gas measures taken within 10 minutes of each other. The researchers looked for "occult hypoxemia"-an arterial oxygen saturation of less than 88% in patients with an oxygen saturation of 92% to 96% on pulse oximetry. Patients self-identified as Black or White.

Almost 11,000 pairs of measurements were obtained from 1,333 White patients and 276 Black patients at the University of Michigan, and more than 37,000 pairs from 7,342 White patients and 1,050 Black patients in the multicenter ICUs. In both groups, hypoxia undetected by pulse oximetry was found in Black patients nearly three times as often as in White patients. In the University of Michigan cohort, occult hypoxemia was evident in 11.7% of Black patients and 3.6% of White patients. In the multicenter analysis, occult hypoxemia was evident in 17% of Black patients and 6.2% of White patients.

While these results indicate inaccuracies in only a subgroup of people of color, they highlight the need for close assessment of the patient's signs and symptoms and other clinical data in the management of COVID-19 and other critical illnesses. The study authors note that "reliance on pulse oximetry to triage patients and adjust supplemental oxygen levels may place Black patients at increased risk for hypoxemia." Patients who are monitoring their own oxygen saturation levels at home, especially people of color, should be alerted to the potential for inaccurate pulse oximeter readings.-Betsy Todd, MPH, RN