What is a pulse oximeter, and does the coronavirus pandemic mean you need one?

Typically clipped over a finger (though a toe or ear lobe works, too), a pulse oximeter transmits light from sensors on one side of the device through the body part to sensors on the other side.

In about 15 seconds, it calculates how much oxygen is being transported through the person’s bloodstream and displays the results as a percentage (abbreviated SpO2).

Doctors consider a SpO2 reading of 94 percent and higher to be normal.

Pulse oximeters are usually purchased for home use by people who want or need to monitor their oxygen supply, including patients with chronic lung conditions such as COPD, performance athletes or people living at higher altitudes.

Shortly after the pandemic began, however, the easy-to-use devices started being touted as a means to detect serious complications from COVID-19, the disease the virus causes.

“The reason there is such great interest in pulse oximeters now is that COVID-19 has a fairly significant effect on the body’s ability to oxygenate, sometimes discordant with how the patient feels,” said Benjamin Seides, director of interventional pulmonology at Northwestern Medicine Central DuPage Hospital in Winfield, Ill., outside Chicago.

Though a patient may not be especially short of breath, a low blood oxygen level may indicate the person is headed for a crisis.

Seides said an idea started to spread: Maybe if physicians told people to watch their blood oxygen levels, they could contact a doctor or go to the emergency room if their saturation levels dramatically dipped. That prompted a run on the devices.

Medical-grade pulse oximeters cost $200 or more, but consumers can find them for $50 to $70 at online stores, big-box stores. Even the lower-cost versions are considered a fast and reliable way to measure how well you are oxygenating.

Correct usage is key to a trustworthy reading, however, which can fluctuate based on a number of factors — what you are doing physically (sitting versus running), proper device placement and the altitude you live at.

Artificial nails and nail polish, especially gel-based, can produce inaccurate measurements of SpO2, as they block light transmission.

Cold hands or poor circulation also can interfere with the light and produce false numbers, because pulse oximeters need a steady flow of blood beneath the sensor.

Pulmonologist Federico Cerrone, managing physician at Overlook Medical Center in Summit, N.J., said people with chronic health issues may want to get a pulse oximeter at this time because it can be a helpful tool for regularly checking in with a doctor via telemedicine.

Patients with COVID-19 who are discharged from a hospital also may be given a pulse oximeter so they can monitor their numbers to see if they are improving or getting worse.

“It can be a reassurance or a harbinger of issues indicating you may need to return to the hospital,” Cerrone said.

Unless you have an underlying condition or are recovering from COVID-19, however, you may not need to add one to your collection of home health supplies.

“It’s a convenience, not a necessity. If you are short of breath or have a cough, you can usually call your physician and have a drive-through check of your oxygenation,” Cerrone said.

He also cautions against the use of oximeter apps that purport to give you various medical readings because their performance has not been validated in scientific studies.

A recent University of Oxford study found no evidence that any smartphone technology is accurate for the measurement of blood oxygen saturation. In fact, the study states, “oxygen saturation levels obtained from such technologies should not be trusted.”

There are potential drawbacks to widespread usage of pulse oximeters.

Some patients become compulsive and check their saturation levels too often.

“In the hands of nervous patients, the device creates anxiety and confusion without much probative value, because even with a small dip in readings they call their physician,” Seides said. “It’s important to recognize that a pulse oximeter is a single data point of a complete picture.”

Another concern is that those who use a pulse oximeter as a COVID-19 litmus test may ignore other troubling signs.

“I worry that though their saturation numbers look OK, people with other symptoms such as a shortness of breath or persistent cough won’t seek medical attention,” Seides said.

Physicians agree that during this pandemic, the important actions remain physical distancing, washing hands, wearing a mask, listening to public health officials and, if you’re not feeling well, calling your doctor.