The Covid-19 pandemic has sparked a sudden interest in the humble fingerprint pulse oximeter, a medical device that lets people check their oxygen saturation levels. The small, handheld units normally attach to your finger or toe, and can be found at many pharmacies and grocery stores for $20 to $50. The devices are typically used by patients with respiratory illnesses to see if their blood oxygen level is low. It’s also used by athletes and pilots who may sometimes need to keep tabs on their oxygen supply.
But many with Covid-19 also experience their blood-oxygen levels dropping to lower than normal.
TV host Andy Cohen, who has recently recovered from Covid-19, told listeners on Andy Cohen Live on March 30 that owning a pulse oximeter was a source of relief for him. “You could scare yourself and think, ‘Oh my God, my lungs don’t feel right,’ but you could use this pulse oximeter and see, ‘OK, well actually, you’re fine, you’re within the range,’” he said.
But interest in pulse oximeters sparked long before Cohen’s tip. Social media and YouTube are filled with tutorials instructing people to buy pulse oximeters in order to monitor whether they have Covid-19. Many models are sold out on Amazon, as well as the online and physical storefronts of Walmart, CVS, and Target.
Sales data provided to Quartz from Bloomreach, an e-commerce software firm, shows that US sales of fingerprint pulse oximeters spiked by 527% on the week of Jan. 20, which is when the first case of Covid-19 was confirmed in the United States. It spiked again in mid-February, and while the rate of increase has gone down, sales have grown every week since then.
Google searches for “pulse oximeter coronavirus” began to spike in mid-February, and they’ve increased every day since then, according to Google Trends.
But doctors and professional medical organizations such as the American Lung Association and the American Thoracic Association are advising otherwise healthy patients to not buy a pulse oximeter.
Doctors normally prescribe pulse oximeters for patients with chronic lung disease, such as emphysema or pulmonary hypertension, who receive supplemental oxygen at home. Such patients need to regularly monitor their oxygen levels, so that they know when to increase the flow rate of their supplemental oxygen.
“There is no good role for a pulse oximeter for an otherwise healthy person who doesn’t have access to [supplemental] oxygen,” said Jamie Garfield, a volunteer medical spokesperson at the American Lung Association and an interventional pulmonologist at the Temple Lung Center in Philadelphia.
When you put your finger inside a pulse oximeter, it shines a beam of light that detects the level of oxygen in your blood. It will then show your SpO2 measurement, which is the percentage of oxygen that your blood is carrying. Doctors consider an SpO2 of 95% and above to be normal. The American Thoracic Society says that most patients need an SpO2 of at least 89% to keep their cells healthy.
If your blood oxygen levels dipped to dangerously low levels, you would know there was a problem. You wouldn’t need a pulse oximeter to tell you.
“You would feel extremely short of breath. Even levels in the lower 90s are not normal for healthy folks and they would know something was wrong with their breathing even without the number telling them,” said Mark Levy, a family physician in Seattle. To put it into perspective, he added, a patient with an SpO2 rate of 88% would require continuous oxygen therapy.
Levy believes that the role of a pulse oximeter during the Covid-19 pandemic is “limited” for most people. Blood oxygen levels are just one of the many vital signs that doctors monitor in patients with Covid-19.
“Most infected people will survive this infection, and will never need a visit with their doctor, let alone hospitalization. For those who are sicker, monitoring pulse, respiratory rate, and other low-tech things like how someone looks and feels may be all that is needed,” said Levy.
And for asymptomatic patients, which may be as much as 25% of those with the disease, doctors warn that an SpO2 reading will be useless.
Not all Covid-19 patients see their blood oxygen levels dip to dangerously low levels, if at all. Two employees from a cruise ship in Japan who tested positive for Covid-19 were studied by doctors at the nation’s Asahi General Hospital. One was a 35-year-old woman, the other a 27-year-old man. Neither had a fever or shortness of breath. Both had oxygen saturation levels of 95%, which is considered on the low end of normal.
Otherwise healthy people can often maintain normal blood oxygen levels for a long time despite being really sick, because their heart and lungs compensate in other ways, according to Andrew Admon, a pulmonologist at the University of Michigan in Ann Arbor. “It’s not unusual for oxygen saturation to stay normal or close to normal, and then drop suddenly. As a result, a normal oxygen saturation can be falsely reassuring,” Admon wrote to Quartz.
But a “pulse ox” could be useful for those with a number of underlying conditions, such as asthma, congestive heart failure, or chronic obstructive pulmonary disease. Cohen, who has asthma, falls under this category. Levy says having additional information such as SpO2 will help doctors manage the disease remotely.
But for everyone else? The device may just be an unneeded source of anxiety. “You might check and check and check, and what are you going to do if the number is low?” asks Garfield.
Hospitals are advising patients who are experiencing Covid-19 symptoms such as shortness of breath, a cough, or fever, to call their doctor, rather than crowd emergency rooms. Covid-19 patients who are in serious enough condition to need hospitalization will have their vitals monitored at that point.
Amazon is currently flooded with listings for pulse oximeters, many of which are not FDA-approved. People who use such devices are at risk of getting an inaccurate reading. A 2016 study in Anesthesia & Analgesia looked at a number of inexpensive pulse oximeters not cleared by the FDA, and found that many of them were prone to large errors.
A number of wearables offer SpO2 features, including ones offered by Fitbit and Garmin. Apps that use your smartphone’s camera to deliver SpO2 measurements can be hit-or-miss. Such technology hasn’t been cleared by the FDA. One study looked at three pulse oximeter apps: iOx, OX, and POx. All three apps delivered inaccurate SpO2 measurements, according to the authors, from the University of Alabama and the University of Michigan.
YouTube is filled with tutorials on how to build your own pulse oximeter. Doctors discourage patients from using homegrown measures, as well as any device that isn’t FDA-approved. “I just think that’s a terrible idea,” said Garfield.
Even pulse oximeters at hospitals have been known to deliver inaccurate results. But hospitals have the ability to use other methods of screening, such as measuring oxygen levels directly, looking at tracing data from the pulse oximeter, and physically examining the patient. “Without the ability to do this, it’d be hard to separate a poor reading due to a faulty homemade pulse oximeter from a true cause for concern,” wrote Admon.
But what can people do in the meantime? Listen to your body, and stay alert for symptoms such as dry coughing, fever, and shortness of breath. If you feel long-winded or lethargic during a period of usual activity, such as showering or getting dressed, that should raise an alarm. “That should trigger people to contact their physician or go to an emergency room, no matter what their oxygen level is,” wrote Admon.