What Is an Arterial Blood Gas Test?

An arterial blood gas (ABG) test measures oxygen and carbon dioxide levels in your blood. It also measures your body’s acid-base (pH) level, which is normally balanced when you are healthy.

You may get this test if you are in the hospital because you have a serious injury or illness.

The test gives your doctor clues about how well your lungs, heart, and kidneys are working. You’ll probably get other tests along with it, too.

Every cell in your body needs oxygen to live. When you inhale and exhale, your lungs move oxygen into your blood and push carbon dioxide out. That process, called gas exchange, gives energy to the body and expels waste.

But if you have a hard time breathing or an illness that affects your lungs, your doctor may use an arterial blood gas (ABG) test to help check on what’s happening with your lungs and other organs.

Why You Get It

Your doctor may request an arterial blood gas test to:

What Happens During the Test?

You are likely to have an arterial blood gas test in a hospital, but your doctor may be able to do it in his office.

Your doctor or another health care worker will use a small needle to take some of your blood, usually from your wrist. They might instead take it from an artery in your groin or on the inside of your arm above your elbow.

Before the arterial blood gas test, your doctor or another health care worker may apply pressure to the arteries in your wrist for several seconds. The procedure, called the modified Allen test, checks that blood flow to your hand is normal.

Also, if you are on oxygen therapy but are able to breathe without it, your doctor may run the arterial blood gas test after your oxygen has been turned off for 20 minutes.


You are likely to find collecting blood from an artery hurts more than drawing it from a vein, because arteries are deeper than veins and there are sensitive nerves nearby. You may have a few minutes of discomfort during or after the test.

You also may feel lightheaded, faint, dizzy, or nauseated while your blood is drawn. To lower the chance of bruising, you can gently press down on the area for a few minutes after the needle comes out.

What Do the Results Mean?

Results of your arterial blood gas test usually are available in less than 15 minutes. But your doctor cannot diagnose a problem with an arterial blood gas test results alone. So you’ll probably get other tests, too.

Arterial blood gas test results may show whether:

  • Your lungs are getting enough oxygen
  • Your lungs are removing enough carbon dioxide
  • Your kidneys are working properly

The values for normal results vary. If your results aren’t normal, there could many reasons why, including certain diseases or injuries that affect your breathing. Your doctor will consider your results in light of your overall health and any conditions you have, as well as other test results, and then recommend your next steps for better health.

WebMD Medical Reference Reviewed by Melinda Ratini, DO, MS on October 04, 2017



American Lung Association: “How Lungs Work.”

National Heart, Lung, and Blood Institute: “Pulmonary Function Tests,” “What to Expect With Blood Tests.”

Mayo Clinic: “COPD: Diagnosis.”

Merck Manual: “Overview of Acid-Base Balance,” “Arterial Blood Gas (ABG) Analysis.”

American Thoracic Society: “Oxygen Therapy.”

American Association for Clinical Chemistry: “Blood Gases.”

© 2017 WebMD, LLC. All rights reserved.