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Pulse oximeter can give inaccurate oxygen readings for people with dark skin. Credit: Afolabi Sotunde/Reuters
Evidence is mounting that devices widely used to measure blood oxygen levels can be inaccurate in people of colour1,2,3. As a result, the US Food and Drug Administration (FDA) plans to propose that companies conduct more stringent evaluation of the devices, called pulse oximeters, before applying for agency approval.
The proposal, which the agency has not yet formally announced, calls on manufacturers to increase both the devices’ accuracy and the number of people on which the devices are tested. The agency also wants companies to test the devices on people whose skin colours span the entire range of a predetermined scale. FDA scientists presented the proposal at a meeting of an independent advisory committee on 2 February.
Researchers who have spent years studying the performance of the devices and the resulting health disparities applaud the FDA’s efforts. “The bar was set so low with the regulatory guidance up until now that there’s low-hanging fruit that can be addressed,” says Michael Lipnick, a global-health specialist at the University of California, San Francisco.
After being clipped onto a fingertip, a pulse oximeter shines light through the digit and measures how much of this is absorbed by the oxygen-carrying molecule haemoglobin, giving a reading of blood oxygen saturation. The measurement, considered one of a person’s ‘vital signs’ alongside factors such as heart rate and temperature, can give physicians rapid insight into a person’s health.
But melanin pigments in dark skin can interfere with the devices (see ‘Prone to error’). As a result, the oximeters can indicate oxygen saturation values higher than those derived using the gold-standard method of measuring oxygen levels — which tests blood taken from an artery — especially in people with low blood oxygen levels.
During the COVID-19 pandemic, studies2,3 found that the devices’ overestimation of oxygen levels can lead to people of colour receiving less treatment, particularly in hospitals that use strict blood-oxygen cut-offs to determine who is eligible for care. “Nobody appreciated that even these small biases could lead to enormous health-care disparities,” Lipnick says.
The disparities have led researchers and advocacy groups to demand that the FDA ensure that the devices, which have historically been calibrated on people with light skin, are accurate in people with dark skin. They have called on the agency to revise its current guidelines — which were published in 2013 — for manufacturers seeking approval for their devices. Those guidelines stipulate that the devices should be tested on at least ten people, at least two of whom must have “darkly pigmented” skin.
Fingertip oxygen sensors can fail on dark skin — now a physician is suing
Fingertip oxygen sensors can fail on dark skin — now a physician is suing
At the advisory committee meeting, FDA scientists proposed that companies instead test the devices on at least 24 people whose skin colours span the entirety of the Monk Skin Tone (MST) Scale, a ten-shade scale that describes the full range of human skin colours. This is an upgrade, says Kimani Toussaint, an optics specialist at Brown University in Providence, Rhode Island, because “darkly pigmented” is subjective. An increase in the number of people tested will also help the FDA to evaluate whether a device’s performance differs with skin colour, he says.
But some advisory committee members, such as Rachel Brummert, a medical-device safety advocate based in Charlotte, North Carolina, questioned whether 24 people would be sufficient. And other scientists say they wish the proposed guidelines recommended that manufacturers test their devices in real-world conditions. “Ideally, the FDA would take a more aggressive step to make sure these devices are evaluated in clinical settings,” says Ashraf Fawzy, a pulmonologist and critical-care physician at Johns Hopkins University in Baltimore, Maryland.
In a statement, the FDA responded that it will continue to research improvements to pulse oximeters and that ensuring that pulse oximeter performance is “equitable and accurate for all U.S. patients” is a “high priority” for the agency.
But more research is needed to understand how skin colour interacts with other variables, such as how much blood flows to the fingers, Lipnick says. And most studies on the topic are based on self-reported ethnicity or skin-colour data; he and his colleagues are now evaluating the performance of the devices using the MST Scale, and investigating whether the MST Scale is the best measure to use for this purpose.
The agency faces a conflict between improving the accuracy of the devices and ensuring that the extra testing it recommends isn't overly cumbersome. The agency cannot suddenly pull the devices from the market when there are no replacements and “such a large volume of patients benefiting from the devices”, says Yadin David, a biomedical engineering consultant in Houston, Texas, who chairs a separate FDA advisory committee on medical devices.
Confronting racism in Black maternal health care in the United States
Confronting racism in Black maternal health care in the United States
There are other solutions beyond taking the devices off the shelves, says Michael Sjoding, a pulmonologist at the University of Michigan in Ann Arbor. He hopes that data about the devices’ performance will be made more readily available to potential purchasers, such as hospital systems, so that they can “weigh the data when they’re making purchasing decisions”.
Lipnick says that the implications of the debate will reverberate around the world, especially in low- and middle-income countries that still struggle to access these devices. If companies find it difficult to comply with new standards, “it could result in products going off the market or prices going up”, he says.
The FDA has not indicated if or when it might move forwards with the proposed changes, nor when the changes would go into effect. The agency typically publishes draft proposals and solicits feedback from the public before finalizing guidance. Sjoding hopes changes are implemented soon. “The longer these changes aren’t made, the longer that patients are put at risk,” he says.
doi: https://doi.org/10.1038/d41586-023-04144-6
Update 03 February 2024: This story has been updated with a response from the US Food and Drug Administration.
Clarification 05 February 2024: The number of people with “darkly pigmented” skin who, according to US Food and Drug Administration guidelines, must be included in testing of pulse oximeters has been clarified.
Sjoding, MW et al.N. Engl.J. Med.383, 2477–2478 (2020).
Fawzy, A. et al.JAMA Intern.Med.182, 730–738 (2022).
Gottlieb , ER , Ziegler , J. , Morley , K. , Rush , B. & Celi , THE PEOPLE Intern.Med.Rev. 182, 849–858 (2022).
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The unseen Black faces of AI algorithms
Fingertip oxygen sensors can fail on dark skin — now a physician is suing
Skin colour affects the accuracy of medical oxygen sensors
Is a racially-biased algorithm delaying health care for one million Black people?
Millions of black people affected by racial bias in health-care algorithms
Confronting racism in Black maternal health care in the United States
Tackle systemic racism to diversify health care and clinical research
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