What Is a Pulse Oximeter and Do You Need One?

By Edo Paz, MD
Medically reviewed checkmarkMedically reviewed
May 14, 2020

One of the most startling findings that some COVID-19 patients demonstrate when they show up in the ER is that their oxygen levels can be extremely low. These levels are much lower than what we see with similar respiratory issues and out of proportion to the degree of shortness of breath they feel. This begs the question, would it be helpful to track blood oxygen levels at home to identify people at the beginning of their COVID illness, before their levels become extremely low? That’s where a pulse oximeter comes in.

What is a pulse oximeter?

A pulse oximeter is a small device that you can “clip” to the tip of your finger and get a reading of your blood oxygen levels. Most pulse oximeters also show your heart rate.

How do I interpret the results?

A normal reading for blood oxygen levels, or “saturation,” is above 95%, although can be lower if you have certain chronic medical conditions (like COPD) or acute illnesses (like pneumonia or COVID). If your oxygen saturation is less than 95%, you should speak with a doctor, like one through the K app. In terms of heart rate, a normal reading is 60-100 beats per minute, although this can go lower in people with good cardiovascular fitness.

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How does a pulse oximeter work?

The pulse oximeter works by sending light with different wavelengths through your finger. A protein in your blood called hemoglobin is responsible for carrying oxygen, and absorbs different wavelengths of light depending on the amount of oxygen bound. The pulse oximeter can thus use the wavelengths absorbed and transmitted to estimate the oxygen saturation in your blood.

Which finger should I use?

It doesn’t really matter which finger you use. What is more important is that your hands are somewhat warm, as this works better than cold hands. Also, note that dark nail polish can affect the reading.

How should I use the pulse oximeter and what are the risks?

You can use the pulse oximeter anytime you want to get some insight into your oxygen levels and heart rate. It is a good idea to get a baseline reading, and you can definitely use the device if you are feeling unwell (cough, fever, etc). If your values drop below 95%, you should reach out to your doctor or chat with one of the doctors through the K app.

The main risk to using this device at home is the potential of receiving an inaccurate result. If the device shows you a low number that is inaccurate, you may seek care that you do not need. If the device shows a number that is too high, you may be inappropriately reassured, although this scenario is less likely. One step you could take to verify a result that does not match how you feel is to ask someone else to use the pulse oximeter to see if their value seems accurate. But when in doubt, you should always reach out to a doctor, including one through the K app.

Which device should I trust?

Home monitors tend to be fairly accurate, but you should always check to make sure the one you are buying is on this database, indicating that the FDA deems it safe and effective. Of note, although some phone apps use the camera to estimate your oxygen saturation, these are generally unreliable.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Edo Paz, MD

Edo Paz is the VP of Medical at K Health. Dr. Paz has two degrees in chemistry from Harvard and earned his medical degree from Columbia University. He did his medical training in internal medicine and cardiology at New York-Presbyterian. In addition to his work at K Health, Dr. Paz is a cardiologist at White Plains Hospital, part of the Montefiore Health System.