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“It was anecdotal,” he said, but doctors began using the clips on the fleshy part of the ears, rather than on a finger, to get better readings.
At U-M, Sjoding and colleagues caring for COVID patients documented discrepancies between oxygen levels recorded on pulse oximeters and the levels measured by arterial blood gas tests from blood draws, which is considered the gold standard for accuracy.
They pulled medical records going back to January 2020, and compared readings among Black and white patients who received both tests. There was a “clear difference” between the pulse oximeter readings of 1,333 white patients and 276 Black patients, said Sjoding, who explained his findings on Nov. 1 to U.S. Food and Drug Administration advisors.
Black patients were nearly three times as likely as whites to have low oxygen readings (88 percent or below) that went undetected by pulse oximeters, according to the 2020 report, published in the New England Journal of Medicine.
The team continued to review more data, with similar results.
In additional studies published this year, Sjoding and colleagues found false pulse oximeter readings were more frequent among Black pediatric patients (21.1 percent of the Black patients had low oxygen levels that showed up as normal on the pulse oximeter). Among white pediatric patients, the error rate was 15.6 percent.
Among Black military veterans the error rate was 19.6 percent, compared with white veterans (15.6 percent). And among Black patients being considered for a specialized lung-blood machine, the error rate was 21.5 percent, double that of whites (10.2 percent).
The explanation for the disparities: Melanin, a natural skin pigment found in higher levels among dark-skinned people, absorbs light, skewing readings among patients of color, Sjoding said.
The implications were self-evident.
“If the oxygen level of an entire population is getting overestimated, the consequence is that people in that population who should have had specific treatments might not be getting them,” he said.
Could flawed oxygen readings have contributed to higher COVID deaths among Black residents early in the pandemic?
“I think it’s certainly a plausible potential explanation,” Sjoding said. “I mean, I think you know, it’s a complex question. And for sure, there’s many other factors at play, but it’s certainly a plausible potential. You know, reason why, or a part of the reason why.”
The results were “jarring” — especially since the older studies had already hinted at the discrepancies, Sjoding recently told STAT, a national news publication that covers health issues.
“I am a pulmonary physician at the University of Michigan. I trained to be a lung doctor. And in my training I didn’t really know about this,” he said.
Early last year, the FDA issued a warning about “limitations and accuracy of pulse oximeters,” citing concerns about, among other things, how skin pigmentation “can affect the accuracy of a pulse oximeter reading.”
Sjoding presented the U-M research — titled, “Hiding in plain sight – Racial Bias in Pulse Oximeters” — to the FDA advisors group that met Nov. 1.
When it comes to pulse oximeter readings, “small differences, at a population level, can have a big impact” in health disparities, Sjoding told the panel.
The advisors ultimately recommended more research on disparities, more testing of devices, and better labeling for pulse oximeters to caution users against flawed readings.
The FDA has not yet acted on the recommendations.
Sjoding said another worldwide event in 2020 — the Black Lives Matter movement — brought the data and the limitations of earlier research into sharper relief. And critics noted that the original testing of pulse oximeters disproportionately relied on light-skinned participants.
“I think there’s just been greater awareness of systemic inequalities,” Sjoding said, and “this technology we’re using (is) working less well in a particular group that’s really sort of suffered a lot, even in the healthcare system.”
Concern for children
To be sure, doctors consider more than a single reading from a pulse oximeter to make critical care decisions, said Dr. Gurbaksh Esch, a pediatrician at Flint-based Hurley Children’s Hospital and co-founder of the Michigan Chapter of the American Academy of Pediatrics’ Health Equity Workgroup.
Pediatricians, for example, will take notice of a baby’s belly retracting, or its nose flaring as it struggles to breathe.
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