OAKLAND, California.

The patient was in his 60s, an African American man with emphysema. The oximeter placed on his fingertip registered well above the 88% blood oxygen saturation level, that signals an urgent risk of organ failure and death.

Yet his doctor, Noha Aboelata, believed the patient was sicker than the device showed. So, she sent him for a lab test, which confirmed her suspicion that he needed supplemental oxygen at home.

Months later, in December 2020, Aboelata thought back of her patient as she read a New England Journal of Medicine article showing that pulse oximeters were three times as likely to miss dangerously low blood oxygen levels in Black patients as in white ones.

At a time when Black Americans were dying of COVID at high rates, hospitals struggled to find beds and oxygen for those needing them. The finding exposed one of the most blatant examples of institutional racism in American health care.

State attorneys general and U.S. senators have pressed the FDA to take steps to eliminate racial bias in pulse oximeters that has caused delays in treatment and worse health outcomes, and more recently has raised concern about the reliability of hospital AI tools that draw on reams of data from the devices.

Aboelata’s clinic has sued producers and stores that sell oximeters, demanding they pull the devices or add safety warnings to the labels. Many of her patients rely on home oxygen, requiring accurate readings for Medicare to cover.

But getting rid of the devices central to care for heart and lung diseases, sleep apnea, and other conditions is no option.

Since the 1990s, convenient fingertip clamps have come to stand in for many uses of arterial blood gas readings. These are the gold standard for determining oxygen levels. Makers of oximeters will sell around $3 billion this year because of their usage in nearly every hospital, clinic, and long-term care facility. During the pandemic, hundreds and thousands of Americans bought them for home use.

One of them was Walter Wilson, a 70-year-old businessman in San Jose who has had two kidney transplants since 2000. Wilson contracted COVID last December but delayed visiting a doctor because his home pulse oximeter readings were in the normal range.

Wilson ended up on dialysis after years of good health, looking to join a class action lawsuit against the device manufacturers.

“Manufacturers have known for years that people with darker skin get bad readings,” he said, “but they tested them on healthy white people.”

After years of little action on the issue, the FDA in 2021 sent a safety warning to doctors about oximeters. It has also funded research to improve the devices and promised to issue new guidelines for making them.

As the FDA polishes draft guidelines, it had hoped to publish by Oct. 1, clinicians and scientists are unsure what to expect. The agency has indicated it will recommend that manufacturers test new oximeters on more people, including a large percentage with dark-pigmented skin.

Because of industry pushback, however, the guidance does not expect device makers to test oximeters under real-world conditions, said Michael Lipnick, a University of California-San Francisco anesthesiologist and researcher.

Hospitalized people are often dehydrated, with restricted blood flow to their extremities. This condition, known as low perfusion — essentially, poor circulation — occurs in cardiovascular disease, which is more prevalent in Black patients.

Pigmentation and poor perfusion work together to degrade pulse oximetry performance, said Philip Bickler, who directs the Hypoxia Research Lab at UCSF. During COVID, Black patients showed up sicker because of all the barriers those patients face in accessing health care. They are nearing death doors, as their perfusion is lower.

The FDA guidance does not expect manufacturers to measure how well their devices perform in patients with poor perfusion. All this means that the FDA’s efforts could lead to devices that work in healthy dark-skinned adults but do “not fix the problem,” said Hugh Cassiere, who chairs a panel for the FDA’s Medical Devices Advisory Committee, at its February meeting.

Although some recent industry-sponsored studies have shown that some devices work across skin tones, research dating to the 1980s has found discrepancies in pulse oximetry

The FDA response was modest. Its regulatory pathway for pulse oximeters clears them for sale if they show substantial equivalence to devices already on the market. In a 2007 draft guidance document, the FDA suggested that tests of new oximeters could include a sufficient number of subjects with dark skin pigmentation, e.g., 30%. However, the final guidance, issued in 2013, recommended at least 2 darkly pigmented subjects or 15% of your subject pool, whichever is larger. The studies were required to have only 10 subjects. And the agency did not define dark-pigmented.

Testing the devices involves fitting patients with masks that control the gases they breathe while simultaneously taking pulse oximeter readings and samples of arterial blood fed into a highly accurate measuring device invented by the late founder of Hypoxia Lab, John Severinghaus

During the pandemic, a medical charity approached the lab about

donating thousands of oximeters to third-world countries. The oximeters it had chosen “weren’t very good,” he said. The lab then set up its ratings page, a consumer report for pulse oximeters.

According to its tests, some expensive devices don’t work; a few of the $35 gadgets are more effective than competitors costing $350. Over a third of the marketed devices the lab has tested didn’t meet current FDA standards.

To investigate whether real-world tests of oximeters are feasible, the FDA funded a UCSF study that has recruited about 200 intensive care unit patients. Study data will be peer-reviewed for publication, Bickler said.

He said the lab did not warm the hands of patients in the study, which is the customary practice of manufacturers when they test their devices. Warming assures better circulation in the finger the device is attached.

It affects the signal-to-noise ratio, Bickler said. Remember when car radios had AM stations, you’d get a lot of static? That’s what poor perfusion does — it causes noise, or static that can obscure a clear signal from the device.

Hypoxia Lab scientists and doctors in the real world can't warm patient's hands. But “the industry people can’t agree on how to handle it,” he said.

Masimo, a company that says it has the most accurate pulse oximeters on the market, would happily comply with any FDA guidance, Daniel Cantillon, Chief medical officer of Masimo, said in an interview.

Even if the FDA can’t please everyone, its anticipated call for more people with darker skin in oximetry tests will assure diversity in developing and testing devices before they come into the market, Lipnick said. “That bar has been too low for decades.”

To assess harm to individuals from faulty oximeter readings is subjective because these errors are often one factor in a chain of events. However, studies at Johns Hopkins University and elsewhere indicated that patients whose oxygen depletion was unnoticed — possibly thousands of them — had delayed treatment and worse outcomes.

Aboelata said a few manufacturers — Zewa Medical Technology, Veridian Healthcare, and Gurin Products — have responded to the Roots Community Health lawsuit by including warnings about their device limitations.

There’s not much she and other clinicians can do in daily practice other than establish a baseline reading with each new patient and be on the lookout for notable drops. Hospitals have tools to check oxygen levels, but correct readings are critical for outpatient care. In 2022, Connecticut enacted a law banning insurers from denying home oxygen or other services based solely on pulse oximetry readings.

But adapting around the crappy device is no solution, said Theodore Iwashyna, Johns Hopkins Bloomberg School of Public Health professor who co-authored the New England Journal of Medicine article. “A less crappy device is the solution.”

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