A home pulse oximeter attached to a person's index finger

One of the most isolating and scary aspects of the coronavirus pandemic is that people who have COVID-19 or suspect they do are often told to monitor their symptoms at home, and to go to the hospital only if they need immediate medical help, particularly if they have shortness of breath. 

But would you recognize emergency-level shortness of breath if you experienced it?

Based on the recent uptick in online sales of pulse oximeters—devices you typically place on your fingertip to measure the amount of oxygen in your blood—many people are looking for help to assess their breathing and make sure they are getting enough oxygen. But some people ordering these devices from Amazon or other retailers have reported long delays.

These devices, which usually cost $25 to $100, use small beams of light that pass through your finger to measure how much oxygen your blood is carrying (also known as your blood saturation level), and your pulse (or heart rate).

More On Coronavirus

Why do blood oxygen levels matter? When you breathe in air, tiny capillaries in your lungs absorb the oxygen, allowing it to enter into your bloodstream. Red blood cells then carry that oxygen to tissue throughout your body, including your brain and other vital organs. A low oxygen level in your blood could lead to low oxygen in your tissues, and, ultimately, organ failure.

Pulse oximeters may be useful because blood oxygen saturation levels that start trending downward could be a sign that your lungs are faltering and that you need to call your doctor.

Some public figures who’ve tested positive for the coronavirus, like CNN’s Chris Cuomo and Bravo’s Andy Cohen, have been using pulse oximeters in the hope of getting a measure of their lung function while they’re quarantined at home.

But are the kind of pulse oximeters you can buy, or in some cases download to your phone, necessary or even reliable?

To look into the question, Consumer Reports talked with physicians, other experts, and the makers of some of these devices, about when they might be appropriate and how to use them properly.

We did not test at-home pulse oximeters, either stand-alone devices or those that are incorporated into some fitness trackers, such as Fitbits. But we did a limited analysis of one app that’s claimed to measure blood oxygen via a cell phone, and found it unlikely to help consumers trying to make a medical determination about their oxygen levels.

Focus on the Trend, Not Specific Numbers

There is little reason for the average, healthy person to have a pulse oximeter at home, the experts said. But there are some aspects of COVID-19 that could make one useful to people who have received a COVID-19 diagnosis or who have symptoms of the disease, says Elissa Perkins, M.D., associate professor of emergency medicine at Boston Medical Center, who is treating COVID-19 patients there.

That’s because sometimes people with the disease have low oxygen levels even before they have shortness of breath, she says. “In COVID-19 patients, we often see that they look comfortable, but their oxygen saturation is significantly worse than normal.” For that reason, she says, a home pulse oximeter “could provide valuable additional information about their disease.”

In general, experts CR spoke with say they tend to start to worry when oxygen saturation levels in an otherwise healthy adult get under 92 percent.

But Perkins and other experts CR spoke with emphasized that people who use a home pulse oximeter should not fixate on specific numbers. Instead use the readings on the pulse oximeter to get a general sense of oxygen levels and if they are trending up or down. And keep in mind several caveats.

To start, home pulse oximeters are not as accurate as those used in medical settings. Most, in fact, are not intended for medical use and have not been put through the same rigorous testing and review as medical-grade oximeters, says Lex Schultheis, M.D., research professor of bioengineering at the University of Maryland in College Park and a former head of the Center for Devices and Radiological Health at the Food and Drug Administration.

Michael S. Lipnick, M.D., assistant professor of anesthesia and critical care at the University of California, San Francisco, who has tested home pulse oximeters, says that while they may not be accurate enough to get FDA approval, they could “be used to monitor trends,” particularly at oxygen saturation levels above 90 percent.

But even then, experts say that you should interpret the readings cautiously and not make any decisions based on them without consulting a physician. “Even a pulse oximeter designated for medical use must be interpreted thoughtfully in the context of other physical signs, patient reported symptoms, and health history,” says Schultheis, who has studied pulse oximeters. “Otherwise, the information may be misleading.”

Albert A. Rizzo, M.D., chief medical officer of the American Lung Association, says that for people at home with symptoms of COVID-19, “patients really should be concentrating on things like their fever, their respiratory rate, pulse, cough, and if they’re getting out of breath doing the normal things they do every day." He adds, “The pulse ox would be one more symptom or sign to add to those other things that may help make a decision about whether you should go to the hospital."

Further, Rizzo says, fixating on pulse oximeter readings “may give you a false sense of security.” That’s because while in some cases oximeters may indeed identify lung problems before you have trouble breathing, it can also go the other way: You could be struggling to breathe but not show low oxygen saturation levels on your device.

Interpreting results can also be challenging, Rizzo says.

For example, he says pulse oximeter readings can vary depending on your age and medical history. So, ideally, you would know your baseline level for the device’s reading to be most meaningful.

Another complicating factor: Elevation. Normal readings are typically lower for people who live significantly above sea level.

Other factors can also interfere with how well a pulse oximeter works, says Georgine Nanos, M.D., a family physician and CEO of the Kind Health Group, a telemedicine service. That includes moving while taking the measurement, wearing nail polish, or having darker skin or unusually cold fingers (because of conditions such as Raynaud’s syndrome, a disorder that causes blood vessels to spasm, typically in the fingers or toes, and limits blood flow to those areas).

“There are so many things that come into play when evaluating a patient—listening to the person and observing them—you can’t really isolate only one thing,” Nanos says. 

Alternatives May Be Less Accurate

A number of wearable wellness devices have built-in pulse oximeters, but they are likely to be even less accurate than home pulse oximeters.

For example, a Fitbit spokesperson told CR that “over-the-counter pulse oximeters measure estimated oxygen levels at the finger, where blood supply is rich and near the surface of the skin.” But Fitbits measure oxygen levels at the wrist, “where there is less blood supply near the surface.” In addition, devices worn on your wrist are more likely to move during measurement than are those on your finger, making the results less reliable.

For those reasons, Fitbit says its devices “are not intended to track the kind of changes in blood oxygen levels that might occur with acute or chronic respiratory problems.” Rather, the pulse oximeter function in Fitbits is primarily intended to monitor interruptions in breathing, particularly during sleep, to help users who may be dealing with sleep apnea.

Garmin, another maker of fitness trackers, said its wearables have pulse oximeter sensors that can gauge a person’s blood oxygen saturation during the day and night, but that “they’re not designed or intended to diagnose or treat any disease or condition.” Like the Fitbits, the Garmin trackers use light beams to measure oxygen saturation in the blood, through sensors on the wrist, rather than the finger.

Apple Watch does not currently have a feature that measures oxygen saturation.

There are also pulse oximeter apps that you can download to your phone. They could be especially appealing now, as home pulse oximeter devices are in short supply.

CR’s testers did a spot check of one such app, called Pulse Oximeter-Heart Rate Oxygen Monitor App, from digiDoc Technologies, which works on iPhones, not Android phones. It is meant to be used by athletes, and clearly states it should not be used for medical purposes.

CR looked at this app because it was the only one we found that could be downloaded and relies on the smartphone itself, and does not have to be connected to a separate device. The app uses the smartphone’s flash and camera to light up and read your pulse and oxygen when you cover both with your index finger.

The app appears to measure heart rate accurately, says Bernie Deitrick, senior test program leader at CR. But the app itself notes it does not measure blood oxygen levels below 93 percent, and will not display those readings.

The app also frequently failed to detect the blood oxygen level, in which case it did not record the reading, Deitrick says. Most important, the oxygen saturation readings varied widely, even in the same session. “Its oxygen readings varied from 93 percent to 100 percent over the course of 15 minutes,” Deitrick says.

Given the app’s limitations and performance, CR agrees with the developer’s advice: Don’t use this app for medical purposes.

The app maker, digiDoc Technologies, did not respond by publication deadline to CR’s request for comment.

Other Ways to Monitor Your Breathing

The experts CR spoke with emphasized that while a home pulse oximeter might be helpful to some people with COVID-19 or symptoms of the disease, the devices aren’t essential. 

For one thing, Lipnick at UCSF says you can get a sense of breathing without any kind of medical device. For example, you can measure your respiratory rate by monitoring how many breaths you take in 30 seconds, and then multiply that by two to get your breaths per minute. And you can measure your heart rate, or pulse, by putting two fingers on the inside of your wrist, counting the beats for 15 seconds, and then multiplying by four to get your heart rate per minute. While baseline heart and respiratory rates vary from person to person, let your healthcare provider know if you notice a sharp rise in your respiratory rate or heart rate. 

If you have a peak flow meter at home, as many people with asthma do, you could also use that, says Rizzo at the American Lung Association. These devices, which look like a cross between a kazoo and a thermometer, measure how fast air comes out of the lungs when you exhale forcefully into it after taking a deep breath. “People with asthma and COVID-19 symptoms who have a peak flow meter and know their baseline level, could use the device to help determine if their lung function is dropping,” Rizzo says. 

But the most important thing to do is to carefully monitor your symptoms, especially coughing, wheezing, shortness of breath, and fever, and to inform your healthcare provider about any worsening. “Paying attention to how you’re feeling is your best guide,” Lipnick says. That’s “going to be the most telling in terms of tracking your health and trying to figure out if you need to go and see a doctor.”

If you develop any of these emergency warning signs for COVID-19, get immediate medical help, per the Centers for Disease Control and Prevention: trouble breathing, persistent pain or pressure in the chest, bluish lips or face, or new confusion or fainting. If you call 911 or the hospital, let the operator know you may have COVID-19 so that responders can prepare appropriately.