Pulse oximeters overestimate O2 saturations in darker-skin patients; FDA acts (again)
But will the new guidance have any greater impact than last time?
Pulse oximeters for healthcare and consumer use are calibrated on patients with lighter skin. Manufacturers have recognized the devices’ suboptimal performance in darker-skinned patients for decades, but they have faced no serious regulatory or legal pressure to act.
In 2013, FDA issued a suggestion that manufacturers test devices on patients “with a range of skin pigmentations.” But the standard was lax: only two darkly pigmented subjects, or 15% of the total pool were needed. According to a 2023 analysis of applications for FDA approval, as late as 2020 manufacturers were complying with a minimum of effort—e.g., testing on 12 subjects, “3 people with medium skin, 6 with light skin, and 3 with dark skin pigmentation.”
FDA also specified no standards for measuring skin coloring, which allowed manufacturers to exclude the darkest-pigmented subjects in whom pulse oximeters perform most poorly.
In 2020 during the Covid pandemic, researchers at the University of Michigan reported in a letter to the New England Journal of Medicine that in 12% of patients with darker skin, pulse oximeters overestimated their oxygen saturation, reading 92 to 96% when arterial blood gases confirmed the true value to be less than 88%. (A similar degree of overestimation occurred in 3.6% of patients with light skin.)
A follow-up paper raised the concern that erroneous pulse oximetry may have led to undertreatment for Covid and increased readmission rates in people with darker skin, and a subsequent paper suggested an increased risk for organ failure or death in patients with unrecognized severe hypoxemia due to false readings.
More than four years later, in January 2025, the FDA released more specific guidance to manufacturers of pulse oximeters, encouraging more rigorous testing standards in patients with dark skin. The suggestions are not legally binding, but could create reputational risk or civil liability for manufacturers who do not comply.
2025 FDA Guidance for Pulse Oximeter Testing
The new guidance suggests testing pulse oximeters on at least 150 people (previously, only 10 subjects were considered adequate) and using objective measurements of skin tone, such as the Monk Skin Tone scale or spectrophotometric measurements.
At least one-quarter of subjects should have dark skin tones, and half of those (one-eighth the total sample) should have very dark skin.
Labeling should reflect that the devices were tested on people with a variety of skin tones.
The guidance is currently in draft form and will be open to public comment before becoming final in March.
The new suggestions “describe the Agency’s current thinking on a topic and should be viewed only as recommendations,” the FDA wrote.
Next Stop: The Courts
Although the FDA’s guidance is not legally enforceable, noncompliance could expose manufacturers to reputational and civil liability.
In 2022, a class-action lawsuit was filed against Apple in New York alleging that the pulse oximeter on Apple Watches was inaccurate in dark-toned patients.
In November 2024, Medtronic reportedly settled a lawsuit brought by an Oakland community health center alleging that the company’s pulse oximeters contributed to harm. Three other defendants also settled, agreeing to change the labeling of their pulse oximeters to warn of the risk of inaccurate readings in dark-skinned people.
The center also sued CVS, Walgreens, GE HealthCare, and five other defendants that have not yet settled, according to the Los Angeles Times.
Why Do Pulse Oximeters Perform Worse In Dark Skin?
Pulse oximeters emit red and infrared light that passes through the fingertip (or another compressed tissue bed) to a sensor on the other side.
As the light passes through the tissue, some of it is absorbed by hemoglobin.
Deoxygenated and oxygenated hemoglobin absorb light at different wavelengths (660 nm and 940 nm respectively).
The algorithm in the pulse oximeter is tuned to recognize pulsating arterial blood as oxygenated, and the non-pulsatile as deoxygenated. Using proprietary algorithms, the ratio of light at varying frequencies that’s absorbed during the pulsatile phase is indexed to an oxygen saturation value, which is displayed.
Darker-pigmented people have more melanin, which absorbs light across a broad spectrum of wavelengths, including red and infrared light.
The algorithms, tuned to patients with lighter skin, tend to process the “missing” light that was absorbed by melanin as having been absorbed by hemoglobin. The algorithm calculates and reports a falsely high oxygen saturation.
But Will They Work in the ICU?
There is no requirement by the FDA that manufacturers test pulse oximeters on critically ill patients, of any skin tone.
That task—requiring simultaneous measurements of oxygen saturation from pulse oximetry and arterial blood gases in hundreds or thousands of patients—will likely fall to academic clinicians, who were the first to identify and report the potential scale of the problem.
References
Pulse Oximeters for Medical Purposes - Non-Clinical and Clinical Performance Testing, Labeling, and Premarket Submission Recommendations. Draft Guidance for Industry and Food and Drug Administration Staff. January 2025. Draft Guidance Document
Morales vs. Apple Inc. U.S District Court Manhattan docket. 2022