What to Know Before You Buy a Pulse Oximeter

You may have seen one clipped to a patient's finger in a doctor's office or hospital. Much like how a thermometer reads your temperature, a pulse oximeter detects how much oxygen is in your blood. And it reads your heart rate too. But unlike a thermometer, which you likely have in your home, these oxygen level testers have been a less common piece of home equipment. Until COVID-19, that is.

As we've become used to self-testing, taking our temperature, and checking for other signs of virus, the pulse oximeter has made its way into many medicine cabinets. Without it, we can't get an accurate picture of how our lungs are faring. Sometimes, it's hard to distinguish milder symptoms from those that warrant emergency medical care, and that's where a pulse oximeter can help.

"Many doctors have been advising patients, especially those with worrisome symptoms or chronic health conditions like heart or lung problems, to buy a pulse oximeter for home to monitor their oxygen levels without trekking to the doctor or (emergency department)," said Sharon Chekijian, MD, MPH, an emergency medicine doctor with Yale Medicine. Also, as people with mild symptoms are often urged to stay home and consult their doctors via telemedicine, the device provides essential data without having to expose a potentially infectious person to other people.

While pulse oximeters are by no means a necessity for the average healthy person (some doctors suggest them if you have preexisting breathing issues like asthma, COPD, or other lung diseases), having one may be helpful if you contract COVID-19. Here's what you need to know if you're interested in buying one.

How Does a Pulse Oximeter Work?

A pulse oximeter (also called a "pulse ox") is a device that measures oxygen levels (or oxygen saturation, or O2 sat) in your blood, according to Johns Hopkins Medicine. Specifically, it measures the peripheral oxygen saturation, since it's detected peripherally (externally) on the finger, toe, or ear. That's important, according to the World Health Organization, because your blood (more accurately, the proteins in your red blood cells called hemoglobin) carries oxygen and delivers it to your tissues, without which they couldn't function.

"The device transmits wavelengths of light to a sensor which calculates your blood oxygen saturation," said George Fallieras, MD, medical director of BioCorRx and doctor at LA Surge Hospital. That wavelength is targeting the hemoglobin, and the light absorbed by the blood varies with the oxygen saturation of hemoglobin. It then transmits a numerical reading, explains the WHO.

Pulse oximeters also measure pulse rate, in terms of heartbeats per minute, showing how well the body's tissues are "perfused" or supplied with blood, and ultimately, the oxygen that the blood transports.

A pulse oximeter can help detect or monitor breathing issues associated with COVID-19 or COVID-19 pneumonia. The device can be especially helpful if you are experiencing shortness of breath with diagnosed COVID-19—either to keep an eye on progress or to determine when it's worth an emergency room visit.

How Do You Use a Pulse Oximeter?

If you're using an at-home pulse oximeter, the device will clip onto your finger, toe, or earlobe. The best way to administer the test is to do so while sitting down, said Dr. Chekijian, and "the best finger to use it on is the middle finger." Remove any nail polish, avoid using it on cold fingers, and sit still in order to get a correct reading. Also, if you use somebody else's device, disinfect it thoroughly before and after use.

In addition to the reading, you'll notice a tracing on the device that looks like an S-shaped smooth, continuous wave, said Dr. Chekijian. "The wave (called a sine wave) varies with your breathing. This means the device is really picking up the right signals. This is especially important if the reading looks low, so you don't misinterpret it." If the reading is low but you see a squiggly line instead of a regular sine wave, you are probably not getting a great reading.

What Is a Normal Pulse Oximeter Reading?

A reading between 95% and 100% is normal, and anything under 94% should be evaluated by a medical professional, according to the WHO. A pulse oximeter reading of anything below 90% is considered a "clinical emergency" and should be treated urgently. A normal heart rate for an adult is between 60 and 100 beats per minute.

"If you do think you have COVID and you're using the pulse oximeter to measure your oxygen level, be sure to make a log of the readings so you can see if there are any changes," Dr. Chekijian suggested. Also, the numbers aren't the only thing you should focus on. She suggested noting how you were feeling at the time of the reading, whether you felt fine or were experiencing shortness of breath, for example.

Are There Any Reasons Not to Use an At-Home Pulse Oximeter?

As with any at-home test, there is always a chance for faulty readings or incorrect use. The WHO acknowledges this and prompts medical professionals to rely on their own clinical judgment versus a reading on the device. If you get a strange reading at home and you're not feeling ill, you can check the device's accuracy on another healthy family member. But if you're uneasy about a reading and how you're feeling, it's best to seek medical attention.

It's also important not to let a good pulse oximeter reading give you a false sense of security if you're feeling unwell. If you're feeling lousy—shortness of breath, cough, fever—and you haven't been diagnosed with COVID-19, it's best to check in with your healthcare provider.

Where Can You Get a Pulse Oximeter?

The devices are sold online, at drug stores, or via medical equipment suppliers.

A word of caution: While there are some apps for smartphones that claim to measure oxygen levels, research from the Oxford COVID-19 Evidence Service Team found that none of them are reliable enough to substitute for the real thing. Instead, stick to at-home finger pulse oximeter devices.

If you don't have a pulse oximeter and you're worried about your levels, check in with your doctor to see if you can get a reading. "If you feel like you can't catch your breath or are winded with activity please visit a minute clinic, urgent care, or call your doctor to see if you can be seen," said Dr. Chekijian. "If it's after hours, call 911 or proceed to the emergency department."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.