Arterial Blood Gases

What is the arterial blood gas test?

An arterial blood gas (ABG) test is a blood test that measures the levels of oxygen and carbon dioxide in your blood. It also measures the balance of acids and bases in your blood (called the pH).

Why is this test done?

This test can measure how well the body uses oxygen and gets rid of carbon dioxide. It may be done to:

• Check how well your lungs are working.
• Check how well oxygen therapy or other breathing treatments are working.
• Get information about whether your blood has the correct balance of acids and bases.

How do I prepare for this test?

There is usually no special preparation for this test. If you are using oxygen therapy, the technician will need to know how much oxygen you are on, for example, 2 liters per minute, and how many minutes or hours you have been on oxygen before the test.

How is the test done?

A small amount of blood is taken from an artery in your arm with a needle. An artery is a vessel that carries oxygen-rich blood from the heart and lungs to the rest of the body. The artery most commonly used for this test is the artery in the wrist where your pulse is usually checked. The blood is tested in a lab right away to get the most accurate results.

Arteries run deeper under the skin than veins. For this reason, this test may cause more discomfort than blood tests that use blood from a vein. Also, it is more important to apply pressure after the test than when blood is drawn from a vein. Firm pressure needs to be applied to the site for at least 5 minutes after the test to stop bleeding. If constant firm pressure is not used, blood can leak from the artery into the tissue and a large bruise can form where the needle went in. The bruise can be quite sore and take several days to go away.

In some cases, you may have a small tube (catheter) put in your artery. The tube can stay there for several days for blood pressure monitoring or frequent arterial blood gas tests. The blood needed for an arterial blood gas test can be taken from this tube without sticking your artery with a needle each time.

Having this test will take just a few minutes of your time.

How will I get the test result?

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

The usual results include measurements of the oxygen level, carbon dioxide level, bicarbonate level, and acid-base balance. Normal values are usually:

• oxygen level (PaO2): 80 to 100 mm Hg (millimeters of mercury)
• carbon dioxide level (PaCO2): 35 to 45 mm Hg
• bicarbonate level (HCO3): 21 to 30 mEq/L (milliequivalents per liter)
• acid-base balance (pH): 7.238 to 7.44.

What if my test result is not normal?

Many health problems can cause abnormal ABG results. Examples of possible causes of an abnormal result are:

• Your body is not getting enough oxygen from your lungs because of lung disease or severe anemia.
• Your body is not getting rid of enough carbon dioxide because of lung disease.
• Your kidneys are not working properly.
• You have had severe vomiting or diarrhea.
• You have chronic heart failure.
• You have diabetes and your sugar is very high.

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions.

If your test results are not normal, ask your healthcare provider:

• if you need more tests
• what you can do to work toward a normal value
• if or when you need to be tested again.