Doctors are recommending high-risk patients have one within reach during COVID-19.
Taking your temperature can let you know if you have a fever, but that’s about it. You could still have a serious infection with a low-grade fever. In short, a thermometer is an important tool to have in your medical cabinet, but it can’t give you a whole picture of your health.
For this reason — especially as the world works to manage the COVID-19 crisis, people have also been turning to another simple tool: a pulse oximeter (or Pulse Ox). This easy-to-use medical device can tell you your oxygen saturation (SpO2) level and your pulse rate (PR) at home. These readings are especially important because one of the core symptoms of COVID-19 is shortness of breath. A low oxygen reading on an oximeter can alert you to the severity of your symptoms before you start having trouble breathing, so you can get medical help before you might realize you need it on your own.
According to the American Lung Association, the device — which you’ve definitely used at your doctor’s office — easily snaps onto your finger and can quickly tell your oxygen level and pulse.
How does an oximeter work?
Dr. Rosa Garcia, a former researcher at the Max-Planck-Institute for Neurobiology, explains, “A cold light source produces a beam of light that travels through your fingertip, which will appear reddish to the eye. By measuring the amount of light getting through the finger, the device can calculate the percentage of circulating oxygen in your blood.”
What the oximeter is doing is targeting hemoglobin, a protein found in your blood. It absorbs wavelengths of light, depending on how much oxygen is in your blood, and can produce a reading in a few seconds (similar to the time it takes to use a thermometer).
How to best use a pulse oximeter to check your oxygen level
You’ll get the most accurate reading if your hand is warm, relaxed, and held below the level of your heart. There is some evidence that the middle finger of a person’s dominant hand (versus the index, or pointer finger, which many doctors use) offers the most accurate reading, according to a recent study in SpringerPlus.
Your oxygen levels can also fluctuate, so you’ll want to take measurements a few times a day to get a sense of what your normal range is. This can help you establish a baseline to compare readings against when you’re not feeling well.
What oximeter reading is considered normal?
In healthy people, Dr. Garcia says, a normal oxygen saturation reading ranges from 95 to 98 percent, although the American Lung Association says a good number is anything over 90-92 percent. The oxygen level may also help you or your doctor determine whether or not you need supplemental oxygen. Of course, your number will be individual to you, per your lifestyle, whether or not you smoke, have long-term health conditions, or are currently sick. People with underlying health conditions might fall below the normal ranges, Dr. Garcia says.
A good resting pulse range is about 60-100 beats per minute, though athletes tend to have a lower resting pulse. “Big deviations from one’s average pulse might be worrying and should be also checked by a professional,” says Dr. Garcia.
She noted that an oximeter can offer two additional readings — for the perfusion index (PI) and respiratory rate (RR). “The first parameter, PI, is the ratio of pulsating blood flow or peripheral blood circulation to static blood in peripheral tissue. Low PI levels (1-5) indicate poor circulation, good PI levels (5-10) indicate normal circulation and excellent PI levels (10-20) indicate above average circulatory health. The respiratory rate is a vital physiological marker and predictor of clinical deterioration. It is another parameter that can indicate breathing deterioration in those infected by COVID-19,” Dr. Garcia says. A healthy RR is 12-20 breaths per minute, while under 12 or over 25 is a warning sign to call your doctor.
What oximeter reading is considered low oxygen?
Hypoxemia, or a low blood oxygen, level occurs when you have an oximeter reading below 90 percent. This would be the time to call your doctor to make a plan in case you need respiratory assistance during COVID-19, as it can be a warning sign before you experience difficulty breathing or shortness of breath.
Should you have an at-home oximeter during quarantine?
There is no official oximeter recommendation from the CDC, but the answer is probably yes, according to Dr. Garcia. “If you are someone suffering from any of the high risk conditions for COVID-19 — that is, if you have respiratory problems, serious heart conditions, severe obesity, diabetes, liver disease, or chronic renal problems and are in need of dialysis, it might be a good idea to use a pulse oximeter in addition to a thermometer to look for early signs of Coronavirus infection.”
Dr. Garcia isn’t alone in her thinking. In a New York Times opinion piece by emergency room doctor Richard Levitan, the case is made for oximeters being used to detect COVID-19 induced pneumonia and hypoxia (a state of oxygen deprivation). “There is a way we could identify more patients who have COVID-19 pneumonia sooner and treat them more effectively — and it would not require waiting for a Coronavirus test at a hospital or doctor’s office. It requires detecting silent hypoxia early through a common medical device that can be purchased without a prescription at most pharmacies: a pulse oximeter.”
Should I buy an oximeter?
Dr. Garcia said that if you are going to look for an oximeter to buy, you’d be wise to search for FDA-approved oximeters, which can range in price (from about $20-$80, or more). It’s also important to know that a more expensive oximeter isn’t necessarily better than a cheaper one. Most are generally reliable, but you might have a hard time getting your hands on one listed in the FDA-approved database right now, especially as demand is high during quarantine. In that case, don’t be tempted to use iPhone app oximeters that promise accurate readings. Generally, these are not accurate and shouldn’t be reached for over a clip-on-the-finger oximeter you’d find in a doctor’s office.
The pulse oximeter isn’t without flaws. Wearing very long artificial nails or dark fingernail polish can throw the reading off, as can dirty fingers or hands.
Another issue? The oximeter cannot distinguish between carbon monoxide and oxygen, so it’s important that you speak with your doctor if you’re a smoker and using the oximeter, according to the American Thoracic Society. For this reason, if you are a smoker, the reading on your oximeter may be higher than your true oxygen saturation.
The most important thing to know is that an oximeter, like a thermometer, is helpful but not fail-proof. Not only are inaccurate readings entirely possible, it’s important for you to pay close attention to your overall health—not just what the screen tells you, especially if you are at risk of contracting COVID-19. Contact your healthcare provider at the first sign that you might need medical attention, and they will advise you on the best next steps for your health.
