Should You Buy a Pulse Oximeter for COVID-19?

pulse oximeter
Photo by Click and Photo / Shutterstock.com

As COVID-19 attacks the human body, its targets seem capricious, even random. Some victims don’t even know they have the disease; others are felled by it after a seemingly mild case.

One hint that a COVID-19 case is about to turn from mild to serious is low blood oxygen level, or SpO2, indicating that the lungs are no longer pushing sufficient oxygen into the bloodstream.

Hospitals usually hook most patients up to a simple device that constantly monitors blood oxygen level, called a pulse oximeter. It looks like a large clip placed on a fingertip, and it measures oxygen levels by passing light through your finger.

Not surprisingly, as word has emerged that low SpO2 levels can be a sign of trouble, there was a run on at-home gadgets claiming to be as good as the FDA-approved hospital pulse oximeters.

Many consumers already have a device in their home — a smartphone, a smart watch, or a fitness tracker — that purports to measure blood oxygen. But do any of these gadgets really work? And are they trustworthy?

I don’t have a great answer for you. This is going to be one of those frustrating “Here’s what we know now, and it’s not enough” kind of stories, but I’ve done a fair bit of homework on this and figured I’d share. Also, I’m continuing to hunt for better answers, and I hope publishing this piece now might help with that.

To read up on the basics of how pulse oximeters work, click here. For a more rigorous explanation, go to the Johns Hopkins Medicine website.

Gadget makers have been taking strides toward blood oxygen level sensors for some time.

Samsung’s Galaxy smartphones added SpO2 measurement back in 2014 (though the firm still doesn’t seem to trust the tool — more on that in a moment). Apple Watches, Fitbits and Garmins all have included hardware and software necessary to take the tests in recent years, and continue to refine them.

In fact, Wareable.com predicted: “Blood oxygen will be huge in 2020.” Right for all the wrong reasons, I’m sure they’d agree.

Blood oxygen levels are interesting to the fitness crowd because hikers who find themselves at high elevations might end up with altitude sickness, which can be predicted by dropping SpO2 levels. The readings are also increasingly interesting to the estimated 20 million or so Americans who suffer from sleep apnea. Fitbit products can track oxygen levels through the night to see if they dip dangerously low.

The arrival of COVID-19 brings home blood oxygen testing to a more acute crisis.

Initially, doctors were telling patients home gadgets weren’t much use — generally, when blood oxygen levels drop, the symptoms are obvious. COVID-19 is a novel virus, however, and breaking a lot of rules. As I covered recently, some COVID-19 patients experience what has been called “silent hypoxia” — dangerously low SpO2 levels — while not exhibiting traditional symptoms, like disorientation, until it’s too late. So, diagnosed and undiagnosed COVID-19 patients alike could benefit from regular SpO2 testing.

The tests are harmless, so medical professionals don’t necessarily frown on home devices. But inaccurate results, in either direction, could cause unnecessary stress and hospital visits or provide a false sense of security.

On YouTube, you’ll find plenty of videos showing civilians and even some health care professionals comparing readings from these gadgets to readings on hospital-grade machines with favorable results. That’s encouraging, but it’s not proof a home device will give you the early warning you’ll need.

The devices would need to be rigorously tested among a carefully selected population sample with varying conditions to prove their efficacy. Most important, they’d need to prove their accuracy on patients who are suddenly very sick, and I found no YouTube videos with that proof – nor would you expect to.

The gadgets have been independently tested, however. I found three studies of smartphone pulse oximeter efficacy. While limited, the tests suggest the gadgets might be useful, if imperfect. I’m waiting for authors of the studies to answer additional questions from me; I suspect they are all very busy.

Smartphone users can use the internal hardware included in their phone itself to shine a light through their finger for the test, or they can buy an external gadget with a finger clip that connects to the phone through a port.

In one study of 48 participants published last year, subjects used a Samsung smartphone with its internal tester, or an iPhone with an external tester, and their results were compared to a medical-grade device. Smartphone readings showed “a moderate, positive correlation,” but the readings were inconsistent, leading the authors to call for more research.

A second study, published in 2018, was more positive. Among 81 healthy children studied, the authors found, “Smartphone-based pulse oximetry is not inferior to standard pulse oximetry in pediatric patients without hypoxia.” The study did find that internal camera-based smartphone tests, employed by Samsung, were inferior to external plug-in probe tests. Again, it’s important to note that this test did not prove the smartphone pulse oximeters work with hypoxia patients.

This third study, from 2019, did involve hypoxia patients and the results were fairly negative. Using an iPhone 5, it found probe-style devices successfully identified hypoxia patients, though 25% were incorrectly classified. On the other hand, it found the onboard reading from the phone were just about useless.

Taken together, those two studies suggest there’s at least moderate value in buying an external device that connects to your smartphone.

Perhaps Samsung’s measured relationships with its internal pulse oximeter feature is instructive. The firm has advertised the feature in the past. But in the past year, the company removed it as a stand-alone tool from its Samsung Health app, much to the consternation of some users. Clever Galaxy owners can still find it within a “stress” test the software includes, but it’s not easy to discover.

I’ve asked Samsung officials to explain this change; if and when I get an answer, I’ll update this story.

Elsewhere, Samsung warns consumers the device is really for novelty use.

“Not intended for use in the diagnosis of disease or other conditions,” the terms and conditions say. “Not intended for use in the detection, diagnosis, monitoring, management, or treatment of any medical condition … any information found … through Samsung Health is made available only for your convenience.”

More from Bob Sullivan:

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