A pulse oximeter attaches to a finger and uses light to detect the level of oxygen in your blood.
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As coronavirus testing efforts continue to ramp up, and face masks are part of everyday life, a tiny diagnostic tool that clips to your finger is quickly becoming a must-have gadget in the fight against COVID-19. It’s called a pulse oximeter, and it checks your blood oxygen level.
The device was already beginning to surge in popularity as the public learned many patients being admitted with COVID-19 often arrive at the hospital with abnormally low oxygen levels. After an op-ed piece in the New York Times last week recommended pulse oximeters could be used to identify the sickest among COVID-19 patients, sales of the devices skyrocketed. At the time of writing, most were sold out in stores and online.
But questions and controversy have arisen around the at-home use of pulse oximeters, which painlessly measure heart rate and oxygen levels. It’s not entirely clear if a pulse oximeter can detect a coronavirus infection, nor whether their widespread use could help curb the spread of COVID-19.
Whether you already have a pulse oximeter or you’re thinking about buying one, here’s what you need to know about what they do, how they work, what the results mean and how accurate they might be.
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Pulse oximeters: Vital signs, at your fingertips
A pulse oximeter is a small medical device that measures heart rate and blood oxygen saturation. It’s usually clipped to your finger, but it can also attach to your ear, nose, toe or forehead. Some are battery powered and provide real-time results on a small LED display on the device itself. Others connect with a wire to a separate vital sign monitor that records even more precise information about your heart rhythm, body temperature and blood pressure using other sensors connected to your body.
How pulse oximeters measure heart rate and oxygen
A pulse oximeter measures your blood oxygen saturation and heart rate by shining a light through your skin and detecting both the color and movement of your blood cells. Oxygenated blood cells are bright red, deoxygenated cells are dark red.
The pulse oximeter compares the number of bright red cells to dark red cells to calculate your oxygen saturation as a percentage. So, for example, a reading of 99% means only 1% of the blood cells in your bloodstream have been depleted of oxygen.
Every time your heart beats, it pushes your blood through your body in a quick pulse (which is why “pulse” is another word for “heart rate”). A pulse oximeter, using light, detects this movement and calculates your heart rate in beats per minute, or BPM.
What’s a healthy oxygen level and heart rate?
According to the Mayo Clinic, a normal pulse oximeter oxygen level reading is between 95% and 100%, and anything less than 90% is considered dangerously low, or hypoxic. Some doctors have reported COVID-19 patients entering the hospital with oxygen levels at 50% or below.
A normal resting heart rate is between 60 and 100 BPM, or beats per minute. Typically, lower is better, as a slower heart rate is usually an indication of a strong cardiovascular system.
Can a pulse oximeter detect COVID-19?
Not exactly. Although many doctors report that patients with COVID-19 are presenting with dangerously low blood oxygen levels, COVID-19 isn’t the only disease that can cause such a problem. Chronic lung diseases, like COPD, asthma and other non-COVID-19 lung infections can also cause a low oxygen count.
A low oxygen reading by itself is not enough to diagnose COVID-19, but your doctor may want to know about it, especially if you notice the level going down over time. And if you’ve been diagnosed with COVID-19, your doctor may want you to monitor your oxygen level to determine if your condition is worsening or improving.
Although medical professionals continue to rely on temperature checks as an indication of a coronavirus infection, many patients with COVID-19 do not have fevers.
Angela Lang/CNET
How accurate are over-the-counter pulse oximeters?
Like with any electronic equipment, not all pulse oximeters are created equal. A 2016 study of low-cost pulse oximeters concluded several inexpensive consumer-grade devices provided highly inaccurate readings.
Some pulse oximeters have been cleared by the FDA, which means they should meet FDA standards for accuracy. Note that there is a distinction between “FDA-approved” and “FDA-cleared,” with “cleared” being the less rigorous of the two. That said, Class II medical devices like pulse oximeters are usually “cleared” rather than “approved.”
You can look for pulse oximeters on the FDA-cleared list by visiting the FDA’s Premarket Notification website and searching for “pulse oximeter” in the Device Name field, with or without a manufacturer’s name.
Although retailers like Amazon and Walmart still have pulse oximeters available, they’re often unbranded and of questionable accuracy.
Angela Lang/CNET
How much should I spend on a pulse oximeter?
In the 2016 study that found most low-cost pulse oximeters to be relatively inaccurate, “low-cost” was defined as costing less than $50. Pulse oximeters that have been cleared by the FDA tend to range in price from around $50 to $60 to well into the hundreds and even thousands of dollars.
Where can I buy a pulse oximeter?
You can still find pulse oximeters on sale online at Walmart, Amazon and eBay, however most of the name-brand devices you’ll find on various best lists, like those at DigitalTrends, The Wirecutter and Consumer Reports, are either sold out completely or on backorder, with shipping estimates weeks or sometimes months away.
This week, the CDC added five more official COVID-19 symptoms for a total of seven, which are detailed here. However, symptoms, vital signs and statistics aren’t the only way to track the pandemic: Memes and social media chatter are relevant data points, too. Depression and anxiety may not be symptoms of the disease itself, but as the pandemic continues, you’re not the only one feeling down about it.