Dangerous inaccuracy
For more than a decade, it’s been known that pulse oximeters — those devices that attach to a fingertip and tell you your blood oxygen levels — likely aren’t as accurate for people with darker skin tones. That’s because the oximeters work by shining light through tissue. Melanin in darker skin absorbs more light, which can lead to inflated readings.
The problem became more urgent during the Covid-19 pandemic, when people rushed to buy pulse oximeters to check whether their blood oxygen levels were dropping. (My household invested in one, although the humble little device has sat in our cupboard unused since the pandemic.)
Oximeters come in various designs, from tiny personal models that can be bought online for less than $15 to medical-grade units with large displays that are usually seen in hospitals. The concern is that these devices, particularly ones for home use that haven’t received regulatory approval, can falsely reassure patients with darker skin that their blood oxygen levels are healthy. That in turn can lead to delayed treatment.
“A lot of health care systems under the duress of the pandemic were using whatever available technology they could get their hands on, which included a lot of — let’s just call them non-medical grade pulse oximeters,” says Daniel Cantillon, the chief medical officer at Masimo, a medical technology company that produces the devices. “They found that there were significant performance issues.”
New research published in the British Medical Journal this month reinforces existing evidence that many home devices don’t work very well for people with darker skin. The study used a type of camera to measure skin tone objectively and examined the results given by five different fingertip monitors. All five gave higher readings for people with darker skin tones.
So, you might ask, is it possible to make pulse oximeters that work for everyone? The short answer is yes. Devices produced by major manufacturers like Masimo, Medtronic and Nonin Medical for use in hospitals are all designed to provide reliable results for dark skin tones.
Where things become more complex is with devices used at home, although there are some (usually more expensive) exceptions. Masimo, for example, received US Food and Drug Administration approval in 2024 for its over-the-counter oximeter, which uses the same technology as its hospital version. “We have always taken the approach that with the medical-grade pulse oximeters that we use in hospitals, those standards should apply to anything that we offer,” says Cantillon.
Last year, it looked like regulatory action would be taken to ensure the accuracy of oximeters used for medical purposes, when the FDA proposed updating their guidance. Yet the draft has not made it through to formal recommendations, meaning patients may still be left with inaccurate devices. — Ashleigh Furlong