Study: Pulse oximeters may misestimate oxygen saturation in darker skin tones

Editor's Note

Pulse oximeters may overestimate blood oxygen levels in critically ill patients with darker skin tones, according to a March 30 article in HCP Live.

The article focuses on the EquiOx study, conducted at the Zuckerberg San Francisco General Hospital between 2022 and 2024. Presented at the American College of Cardiology (ACC) 2025 Annual Scientific Sessions, the study found that pulse oximeter readings do not perform consistently across different skin pigment categories.

These findings are based real-world experiences with 631 intensive care unit (ICU) patients with an average age of 62 years. As detailed in the article, researchers compared pulse oximeter estimates of blood oxygen saturation with arterial blood gas analysis, considered the gold standard. They collected skin pigmentation data using both the Monk Skin Tone Scale and a spectrophotometer, classifying patients into light, medium, and dark pigment groups.  

Results show that pulse oximeters generally underestimated oxygen levels, but the extent of this bias varied by skin pigmentation. Patients with darker pigmentation showed a less negative bias, but they also faced a higher risk of an overestimate compared to those with lighter pigmentation. This could result in undetected hypoxemia and negative impacts on clinical decisions relying on pulse oximeter readings.

“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,” Carolyn Hendrickson, MD, an associate professor of medicine at the University of California, San Francisco, reported to the conference. “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.”

The article further outlines how these findings challenge previous assumptions that pulse oximeters uniformly underestimate oxygen levels. Hendrickson and colleagues call for further study, arguing that this uncertainty should inform how future devices are tested and regulated. “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 reportedly emphasized at the conference. “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.”