What Is Pulse Oximetry?

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

Why Would I Need This Test?

It can:

  • Diagnose symptoms like shortness of breath
  • Track your blood oxygen level during surgery
  • Manage a heart or lung condition that could affect your blood oxygen levels, like heart failure, COPD, asthma, or pneumonia
  • Show if you need extra oxygen when you exercise
  • Show whether your breathing stops while you sleep, a condition called sleep apnea

If you already use supplemental oxygen, you can do this test at home to make sure your oxygen flow is OK.

What Happens During the Test?

You may get this test during a doctor 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.

How Do You Prepare?

You don't have to do anything special to get ready for this test.

The test results might not be correct if your fingers are dirty, your nails are too long, or if your nails are covered in dark polish. The nurse may ask you to wash your hands, take your nail polish off, or trim the nail on the finger they’re testing.

Ask your nurse if you have any questions or concerns.

What Do the Results Mean?

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.

How Much Does It Cost?

Your doctor usually bills pulse oximetry as part of surgery or other tests they do. You can buy home pulse oximeters online or at a drugstore. They cost between $15 and $80, but some insurance companies will pay for it.

What Are the Risks?

Pulse oximetry is a safe test. There are no real risks. Sometimes the sticky material on the probe might irritate your skin. If your nurse doesn’t put the sensor on the right way, you may not get an accurate result.

Ask your doctor if you have any questions or concerns.

WebMD Medical Reference Reviewed by Minesh Khatri, MD on July 11, 2019



American Lung Association: "Pulse Oximetry."

American Society of Hematology: "Blood Basics."

American Thoracic Society: "Pulse Oximetry."

CHOC Children's: "Pulse Oximetry (Pulse Ox)."

Johns Hopkins Medicine: "Pulse Oximetry."

University of Iowa Stead Family Children's Hospital: "Pulse oximetry."

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