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People with darker skin are 32% more likely to have pulse oximeter readings overestimate oxygen levels, report says

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Scientists have long known that pulse oximeters are less accurate when used for people with dark skin tones – and now, a new report offers some insight into just how much more inaccurate these fingertip clamps can be.

Pulse oximeters are electronic devices that clamp onto a patient’s finger to estimate their blood oxygen levels and pulse rate. Prescription and over-the-counter versions of these devices became popular during the Covid-19 pandemic, but a growing body of research reveals racial disparities in how precise the technology can be.

Black people in the hospital are 31.9% more likely than White patients to have pulse oximeter readings that overestimate their oxygen levels by at least 4 percentage points, according to data published Wednesday in the journal Epic Research, which is owned by the health care software company Epic.

The researchers – from Epic, the University of Maryland Medical System and the Federation of American Scientists – noted in the new report that “providers often order supplemental oxygen or other treatment when oxygen saturation drops below 88%.”

But if a pulse oximeter inaccurately shows a patient’s blood oxygen reading to be much higher than 88% “there may be a delay in potentially life-saving treatment, which could result in significant risk to the patient.”

Pulse oximeters work by sending light beams through someone’s finger to estimate the oxygen saturation of their blood and their pulse rate. Ongoing research has found that if these devices are not calibrated for dark skin tones, the pigmentation of the skin could affect how that light is absorbed by the device’s sensors, leading to inaccurate oxygen readings.

Within the Black community, people have a wide variety of skin colors, but for the new report, the researchers used race as a proxy to examine biases in pulse oximeters.

The report included data on more than 13,000 patients from multiple hospitals in the United States between January 2016 and November 2023. For each person, the data included a pulse oximeter reading and a blood gas oxygen saturation result from blood drawn directly from the patient, taken within five minutes of each other.

The researchers found that 24.7% of Black patients had pulse oximeter readings that were at least 5 percentage points higher than the oxygen levels in their blood gas results. The share of White patients who had such discrepancies in their oxygen readings was 19%.

“We weren’t surprised,” said Dr. Roderick King, senior vice president and chief diversity, equity and inclusion officer at the University of Maryland Medical System, one of the authors of the new report.

“We’ve noticed even before Covid that the pulse ox inaccuracy was there for darker-skinned patients. But what was the most dramatical or most impactful part of this article was that we could quantify using a large dataset of how much it was inaccurate,” he said. “It drives home the importance of understanding how we look at equity and patient care, or health equity.”

The data also showed that 10.2% of Black patients had pulse oximeter readings at least 15 percentage points higher than their blood gas readings, compared with 7.3% of White patients.

“Broadly, what this does is tells us, in a much larger population and in a general sample of patients out there, that pulse oximeters continue to be substantially biased and substantially under detect major problems in Black patients,” said critical care physician Dr. Theodore J. Iwashyna, Bloomberg Distinguished Professor at Johns Hopkins University, who was not involved in the new report but has been closely following research on pulse oximeters.

“The real value of this report is that it shows in your average hospital around the country this is happening,” he said. “Pulse oximeters are substantially failing to detect when patients aren’t getting enough oxygen. This reenforces data that we’ve had since 1990.”

The pulse oximeter was invented in 1974, and a growing body of research dating to the 1980s shows that flawed readings among Black and brown patients can be a real and life-threatening issue in medical care.

One study on flawed pulse oximeter readings, published in 2022, found that among more than 3,000 hospitalized patients receiving intensive care, those who were Asian, Black and Hispanic received less supplemental oxygen than White patients and that that was associated with differences in their pulse oximeter readings.

Another paper published in 2022 said that when compared with White patients, Black patients had higher odds of having low blood oxygen recorded in their blood-drawn readings but not detected by pulse oximeters.

A study of about 7,000 Covid-19 patients, also published in 2022, found that pulse oximeters overestimated oxygen levels in the blood by an average of 1.7% for Asian patients, 1.2% for Black patients and 1.1% for Hispanic patients, compared with White patients. That overestimation may have contributed to delays in patients receiving certain Covid-19 therapies.

Last month, a panel of experts for the US Food and Drug Administration held a meeting to review ways to better evaluate the accuracy and performance of pulse oximeters in patients with dark skin tones.

The FDA Anesthesiology and Respiratory Therapy Devices Panel focused on how to ensure that pulse oximeters perform accurately for all skin colors before they hit the market. The panel recommended that clinical trials for pulse oximeters include more diverse groups of participants across all skin tones.

The panel met in November 2022 to review clinical data about the accuracy of pulse oximetry in people with darker skin and to discuss recommendations on using these devices on people with dark skin tones and whether they should have labels – such as black box warnings – noting that inaccurate readings may be associated with skin color.

“I really hope that maybe this report will be the one that finally gets the FDA to release new, effective regulations – and pulse oximetry companies to produce new devices that function better and more equitably,” Iwashyna said of the new report. “My colleagues and I need better tools to provide our patients the care they need.”

Some of the companies behind pulse oximeters, such as Medtronic, have focused on education efforts to inform users about potential inaccuracies when pulse oximeters are used on dark skin tones – but they have not gone as far as issuing recalls for the products.

“Currently, we think that if there was a recall by any manufacturer around this, we would undermine public safety, because this is a foundational device in operating rooms, in ICUs, in ERs and ambulances,” Dr. Sam Ajizian, chief medical officer of patient monitoring at Medtronic, told the FDA panel in last month’s meeting.

“We continue to evaluate, and we do feel that the benefits of the products in the field far, far outweigh the risks,” he said.

In 2021, the FDA issued recommendations for patients, caregivers and health care providers to be aware of the limitations of pulse oximeters and how the devices may be less accurate in people with dark skin tones.

“Although pulse oximetry is useful for estimating blood oxygen levels, pulse oximeters have limitations and a risk of inaccuracy under certain circumstances that should be considered,” the recommendations said. “Be aware that multiple factors can affect the accuracy of a pulse oximeter reading, such as poor circulation, skin pigmentation, skin thickness, skin temperature, current tobacco use, and use of fingernail polish.”

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