How to Use a Pulse Oximeter

The COVID-19 pandemic introduced at-home medical devices to the general public that most of us weren’t familiar with in the past. A big one? Pulse oximeters.

In case you’re not familiar with it, a pulse oximeter is an electronic device that measures your heart rate, along with the amount of oxygen in your red blood cells, according to the American Lung Association (ALA). It’s easy to use a pulse oximeter: Just clamp the device onto your finger and you’ll get results in a few seconds.

But how do pulse oximeters work and what can they tell you? Here's what you need to know.

How does a pulse oximeter work?

The pulse oximeter works by shining light through your fingertip to look at hemoglobin, the protein in your red blood cells that carries oxygen from your lungs to cells in the rest of your body, explains Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York.

“If the hemoglobin has more oxygen, it absorbs more infrared light; When it has less oxygen, it absorbs more red light,” Dr. Russo says. “The differences in light absorption are then measured on the other side of the clip to give you a calculated oxygen saturation.”

A pulse oximeter can be helpful for tracking your blood oxygen saturation across a range of health conditions but, in the case of COVID-19, it “can allow one to know if the shortness of breath they are experiencing during COVID is associated with abnormal blood oxygenation levels and thus prompt a person to seek medical attention if abnormal readings are obtained,” says Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security.

How do you interpret your pulse oximeter reading?

After a few seconds, the pulse oximeter will give you a reading. This is a two-digit number in the form of a percentage. A reading of 99 percent means that 99 percent of your hemoglobin is carrying oxygen, Dr. Russo says. Normal readings are typically anywhere from 95 percent and up, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine.

But, if you’ve been tracking your blood oxygen saturation levels and notice they’re dipping, it’s time to rope in your healthcare provider. “If you get consistently below 95 percent, you ought to contact your healthcare provider so you’re on the same wavelength,” Dr. Schaffner says. “You don’t want to wait until it’s below 90 percent.”

A few things can throw off your reading, though. “Fingernail polish can interfere with measurement and should be removed for optimal use,” Adalja says. Having a darker skin tone may also lead to you having higher readings than what your body is actually experiencing, he says. (Talk to your doctor about next steps if you suspect that’s happening to you.)

A pulse oximeter can’t diagnose COVID-19 and won’t diagnose COVID pneumonia, but it can alert you that you may need to receive supplemental oxygen, Dr. Russo says.

So, which brand of pulse oximeter is the best? It depends on what you’re looking for. Just know this: If you’re taking regular readings and the numbers are consistent, the results should be correct. “Pulse oximeters are generally thought to be accurate,” Dr. Schaffner says. “They’re even used in hospitals.”

These are the top five pulse oximeters on the market.

Our Top Picks

• Best Pulse Oximeter Overall: LPOW Pulse Oximeter
• Best Easy to Read Pulse Oximeter: Equate Fingertip Pulse Oximeter
• Most Comfortable Pulse Oximeter: ChoiceMMed Pulse Oximeter
• Best Pulse Oximeter With Extra Data: Innovo Deluxe iP900AP Fingertip Pulse Oximeter
• Best Inexpensive Pulse Oximeter: Zacurate Fingertip Pulse Oximeter