Arterial Blood Gases

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

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.
• Provide information about whether your blood has the correct balance of acids and bases.

There is usually no special preparation for this test. If you are using oxygen therapy, be sure to tell the technician 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.

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 collected in tubes and 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.

Because blood pressure is stronger in arteries than in veins, the puncture hole from the needle may take longer to close. Firm pressure is applied to the site for at least 5 minutes after the test to stop bleeding. If firm pressure is not used, a large bruise can form where the needle went in. The bruise can be quite sore and take several days to go away.

Having this test will take just a few minutes of your time. There is no risk of getting AIDS, hepatitis, or any other blood-borne disease from this test.

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

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

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

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 diabetic ketoacidosis, which can happen when 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 health care provider about your result and ask questions.

If your test results are not normal, ask your health care provider:

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