What Is Pulse Oximetry?

Medically Reviewed by Minesh Khatri, MD on May 14, 2023
Written by Stephanie Watson
4 min read

Pulse oximetry, or pulse ox, is a quick, inexpensive, and needle-free test that measures the amount of oxygen in your blood. It shows whether your heart and lungs supply enough oxygen to meet your body's needs.

Red blood cells carry oxygen from your lungs to your organs. But lung or heart disease can lower the amount of oxygen in these cells. When it drops too low, your body doesn’t work as well as it should. Your heart, brain, and other organs need oxygen to do their job.

Your doctor can use this test to find out if you need to breathe in extra oxygen through a tube (your doctor may call it supplemental oxygen) or to be treated for a heart or lung problem.

Your doctor will use pulse oximetry whenever they think that your blood-oxygen levels could be too low. The device can help:

  • Diagnose symptoms like shortness of breath
  • Track your blood oxygen level during surgery
  • Test oxygen levels when you use supplemental oxygen
  • Show if you need extra oxygen when you exercise

You might need pulse oximetry if you have:

You may get this test during a doctor's visit or hospital stay.

Your nurse will put a small, clip-like device called a pulse oximeter on your finger, toe, or ear. Or they’ll put a sticky disposable probe on your finger, nose, toe, or forehead.

The pulse oximeter uses a special type of light to see how much oxygen is in the red blood cells traveling through the blood vessels under your skin.

The test is painless and quick. In just a few seconds, the device will show your heart rate and oxygen saturation level -- the percentage of your red blood cells carrying oxygen. It also measures your heart rate.

Your nurse will take the clip off if it’s just a one-time check. During surgery or a sleep study, it may stay in place to track your blood oxygen.

You should be able to go home after pulse oximetry unless you need to stay in the hospital for a procedure or more monitoring. Your doctor will let you know what happens next and what to do after the test.

Some people use pulse oximeters at home, particularly since the COVID-19 pandemic. (COVID-19 can weaken your lungs and lower your blood-oxygen levels.)

There are two main types of home pulse oximeters:

Over-the-counter oximeters. This is the most common type for home use. You can buy them online or in stores. Some link to smartphone apps as well.

The FDA doesn't review these devices and recommends against using them for medical purposes.

Prescription oximeters. These are the same as those used by hospitals and doctor offices. You can get one with a prescription from your doctor. The FDA reviews these devices to make sure they fall within acceptable ranges of accuracy. 

You can buy OTC pulse oximeters for between $15 and $80. Prescription oximeters are more expensive. Some insurance companies will pay for a pulse oximeter. Check with your provider.

Follow guidance from your doctor and the device manufacturer on how and when to take a reading. You can help improve your chances of accurate and useful readings if you:

  • Make sure your hand is relaxed, warm, and below heart level.
  • Remove any fingernail polish on the finger you’re reading.
  • Place the device exactly how the manufacturer's instructions suggest.
  • Look for one steady number. (Numbers might jump around for a few seconds.)
  • Keep track of your levels along with the date and time to give your doctor a sense for how your numbers change over time. (Levels that get lower over time could suggest a serious health issue).

A blood oxygen level lower than 89% means you may not have enough oxygen in your blood to meet your body's needs. This could be because there’s a problem with your heart or lungs. If your levels are low, you may need to breathe in extra oxygen through a tube. Levels that are a little higher (in the low 90s)might still be abnormal if no other medical history to explain it.

But a pulse oximeter reading is simply an estimate. For example, a reading of 90% oxygen saturation on an FDA-approved prescription machine could mean anything from 86% to 94%. In addition, a number of other things can affect the accuracy of the reading, including:

  • Bad circulation
  • Fingernail polish
  • Long or dirty fingernails
  • Tobacco use
  • Different pulse oximeter sensors (finger clip vs. adhesive) 
  • Skin thickness
  • Skin temperature
  • Skin color: One study shows that dark skin (in African-American people, for example) may get less accurate measurements on current devices.

Other symptoms of low oxygen include:

  • Difficulty catching your breath
  • Bluish color in nails, face, or lips 
  • Racing pulse
  • Tightness or pain in chest
  • A cough that gets worse over time
  • General feeling of discomfort and restlessness 

Call your doctor right away if you notice any of these symptoms, no matter what readings you get on your home device.

A pulse oximeter reading is just one of many signs of your health. Pay attention to all of your symptoms and tell your doctor about anything that concerns you, especially if you have an underlying health condition like lung disease.

It’s also important to know that some people with low oxygen might not show any symptoms. Only your doctor can determine whether you have low oxygen levels (which they might call hypoxia).

Pulse oximetry is a safe test. There are no real risks. But:

  • Sometimes the sticky material on the probe might irritate your skin.
  • If you or your nurse don’t put the sensor on the right way, you may not get an accurate result.

Talk with your doctor if you have any questions or concerns.