Skin Pigmentation May Impact Capability of Pulse Oximeters

Pulse oximeter estimates of blood oxygen saturation levels and traditional measurements of oxygen saturation in arterial blood significantly diverged by skin pigment in critically ill adults in the EquiOx study, according to new research presented at the American College of Cardiology (ACC) 2025 Annual Scientific Sessions.1

These data from a large prospective real-world study showed an overall bias toward an underestimate of blood oxygen with pulse oximeters, while people with darker pigmentation reported less negative bias and a greater risk of an overestimate, compared with a lighter pigment.

“Although pulse oximeter bias on average was negative for all people, it was less negative in the darkly pigmented people than in the people with lighter pigment, meaning that pulse oximeters do not perform the same across different skin pigment categories,” said Carolyn Hendrickson, MD, an associate professor of medicine at the University of California, San Francisco.2 “We also found that the proportion of positive bias—the one that goes in the worrisome direction, meaning that someone might have dangerously low oxygen saturation that is not detected with a non-invasive monitor—was higher in patients with dark skin pigment compared to those with medium and light skin pigment.”

Blood oxygen saturation is used in clinical settings to triage patients and determine treatment decisions, including administration of supplemental oxygen or hospital admission. During the COVID-19 pandemic, Hendrickson and colleagues noted blood oxygen saturation became a popular topic when some evidence pointed to false reassurances about critically ill patients’ health status, with an overestimation of oxygen saturation in certain racial groups.3

This real-world study compared pulse oximeter readings with functional oxygen saturation from blood gas analysis, considered the gold-standard blood test for oxygen saturation. Investigators enrolled 631 patients, with an average age of 62 years, who received treatment in the intensive care unit at the Zuckerberg San Francisco General Hospital between 2022 and 2024.1

Patient demographic data showed nearly one-quarter identified as White, while one-quarter identified as Hispanic, one-fifth as Black, and one-fifth as Asian. Each participant’s skin pigmentation was measured by the subjective Monk Skin Tone Scale and objective measurements of melanin content with a spectrophotometer.

More than half (53%) of patients were classified as medium pigmentation, with 33% having light pigment and 14% classified as darkly pigmented. Simultaneous pulse oximeter and blood gas analysis readings combined for a total of 1760 paired measurements among 631 study participants.

Contrasting with previous data, these results showed pulse oximeter readings often underestimated blood oxygen levels, but identified a positive bias in overestimations of oxygen saturation in 20% of observations, with differing proportions across skin pigment groups.2

Investigators accounted for more than 30 factors potentially influencing blood oxygen saturation levels, including demographics, comorbidities, medications, and physical attributes. After adjustments, the overall trends remained the same, with a bias toward underestimates with a pulse oximeter. However, those with darker pigmentation continued to show less negative bias and a greater likelihood of an overestimate.

The team noted that many oxygen saturation readings were in a relatively high range (>90%), making it unclear whether the same patterns would be seen in patients with lower oxygen levels. Notably, only a small portion of study participants had very dark pigmentation.

Hendrickson and colleagues highlighted the importance of this uncertainty in pulse oximeter readings to inform how future pulse oximeter devices are tested and regulated. They called for further prospective studies incorporating more darkly pigmented patients and observations in lower oxygen saturation ranges to unveil patterns in pulse oximetry bias.

“We think that the social construct of race is important and impacts health outcomes, and it is not the same thing as skin pigmentation,” Hendrickson said.2 “We’re advocating for the use of skin pigment data to be collected in addition to race when trying to understand equitable performance in a variety of patient populations.”

References

1. Hendrickson C, Lipnick M, Chen D, et al. Pulse Oximeter Performance Varies by Skin Pigment. Presented at: American College of Cardiology (ACC.25) Annual Scientific Session. March 29 – 31, 2025. Chicago, Il.

2. Pulse oximeter performance varies by skin pigment. American College of Cardiology. March 30, 2025. Accessed March 30, 2025. https://www.acc.org/About-ACC/Press-Releases/2025/03/30/12/44/Pulse-Oximeter-Performance-Varies-by-Skin-Pigment.

3. Sudat SEK, Wesson P, Rhoads KF, et al. Racial Disparities in Pulse Oximeter Device Inaccuracy and Estimated Clinical Impact on COVID-19 Treatment Course. Am J Epidemiol. 2023;192(5):703-713. doi:10.1093/aje/kwac164