What Is an Arterial Blood Gas Test (ABG)?
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 usually in balance when you’re healthy.
You may get this test if you’re in the hospital or if you have a serious injury or illness.
Every cell in your body needs oxygen to live. When you breathe in (inhale) and breathe out (exhale), your lungs move oxygen into your blood and push carbon dioxide out. That process, called gas exchange, gives energy to your body and gets rid of waste.
But if you have a hard time breathing or have an illness that affects your lungs, your doctor may use an arterial blood gas (ABG) test to help check what’s happening.
Why Is an Arterial Blood Gas Test Done?
Your doctor may ask for an arterial blood gas test to:
- Check for severe breathing and lung problems such as asthma, cystic fibrosis, or chronic obstructive pulmonary disease (COPD)
- Check how treatments for your lung problems are working
- Check whether you need extra oxygen or other help with breathing
- Check your acid-base balance if you have heart or kidney failure, uncontrolled diabetes, severe sleep problems, or severe infections, or if you’ve had a drug overdose
What Happens During an Arterial Blood Gas Test?
You are likely to have an arterial blood gas test in a hospital, but your doctor may be able to do it in their office.
Your doctor or another health care worker will use a small needle to take some of your blood, usually from your wrist. Sometimes they take it from an artery in your groin or on the inside of your arm above your elbow.
Before the arterial blood gas test, they 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.
In order to prepare for an arterial blood gas test, tell your doctor about all medications, supplements, and vitamins you’re taking.
If you’re on oxygen therapy but are able to breathe without it, they might turn off your oxygen for 20 minutes for a “room air” test before the blood gas test.
You may have a few minutes of discomfort during or after the test. Collecting blood from an artery typically hurts more than drawing it from a vein. Arteries are deeper than veins, and there are sensitive nerves nearby.
You also may feel lightheaded, faint, dizzy, or nauseated while your blood is drawn. To lower the chance of bruising, you can gently press on the area for a few minutes after the needle comes out.
Arterial Blood Gas Test Risks
Any test that involves using a needle carries some risks, including bleeding, infection, and bruising. You might have some soreness where the needle went in.
Arterial Blood Gas Test Results
Results of your arterial blood gas test usually are available in less than 15 minutes. But your doctor can’t diagnose you based on an arterial blood gas test alone. So you’ll probably get other tests, too.
Your 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 numbers for normal results vary. There could many reasons why your numbers might be not be in this range, including 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.