What’s the Deal With Pulse Oximeters?
By: Yasmin Tayag
Tags: Health, Quick Q And A, Pulse Oximeter, Coronavirus, Covid 19

What’s the Deal With Pulse Oximeters?

Here’s what to know about devices that can measure blood oxygen saturation

Pulse oximeters measure the percentage of your red blood cells that are carrying oxygen by beaming different wavelengths of light into your finger after it’s clipped on. Photo: Smith Collection/Gado/Getty Images

People showing up at the ER with suspected Covid-19 tend to have an especially concerning symptom, explained emergency room physician Dr. Richard Levitan in the New York Times this month: Pneumonia caused by Covid-19 comes with dangerously low oxygen levels that sometimes go unnoticed. This symptom is known as “silent hypoxia,” wrote Levitan, “‘silent’ because of its insidious, hard-to-detect nature.”

The silence is worrying because it means people might be suffering from Covid-19 pneumonia without even knowing it. To detect silent hypoxia early enough to get treated for Covid-19 pneumonia, Levitan said people could use a home pulse oximeter, a small device for measuring blood oxygen saturation that can be purchased at a pharmacy.

That’s not to say that you should go out and buy one immediately. As one San Francisco physician noted in The Guardian, they “aren’t necessary” for people who are healthy and don’t have other Covid-19 symptoms. In Quartz, an interventional pulmonologist said there “is no good role” for a pulse oximeter if you’re a person who is healthy and doesn’t have supplemental oxygen on hand. Pulse oximeters are normally recommended for people with chronic lung disease who have to monitor their fluctuating oxygen levels; these people usually have devices for delivering extra oxygen into their lungs.

However, a pulse oximeter could be helpful for people who suspect they have Covid-19 but are not sure whether they should go to the hospital, or for those who have tested positive for Covid-19 but felt their symptoms were otherwise mild. A low oxygen reading would suggest silent hypoxia caused by Covid-19 pneumonia, a symptom that requires hospital treatment. This very useful New York Times Q&A on pulse oximeters described the story of one Philadelphia emergency room physician who had stayed home after testing positive for Covid-19 but checked herself into the hospital after she got a pulse oximeter reading of 88% blood oxygen saturation, which fell below the “healthy” cutoff of 92%.

Should you decide to buy one — and there’s no dearth of reviews from sites like the The Strategist and Wirecutter — it helps to know the basics. A pulse oximeter, which looks a bit like a plastic clothespin, measures the percentage of your red blood cells that are carrying oxygen by beaming different wavelengths of light into your finger after it’s clipped on. According to the American Lung Association, a “good number” for your blood oxygen saturation would be over 90% to 92%.

Some key caveats: The accuracy of pulse oximeters varies, readings can differ depending on what finger you use (and if you’re wearing dark nail polish), and, perhaps most critically, it’s not a single reading that matters but the trend — if there is one. If you do use a pulse oximeter, it can be helpful to take multiple readings per day to establish a baseline and take note of any downward trends.

Most importantly, pulse oximeter readings shouldn’t distract you from the established symptoms of Covid-19, listed in full in this handy chart from Elemental. Even if you get a “good” oxygen saturation reading, severe symptoms like chest pain, high fever, or severe shortness of breath warrant a call to your health care provider.