Patient education: Arterial blood gas test (The Basics)

What is an arterial blood gas test? — This test measures the amount of oxygen and carbon dioxide in the blood. It also measures the "pH" or acidity of the blood.

"Arterial" means that the test is done on blood from an artery. Arteries are a type of blood vessel. They bring blood from the heart to the rest of the body.

This test is sometimes called an "ABG test" or a "blood gas."

Why might I need an arterial blood gas test? — Your doctor might order this test:

●To check your oxygen and carbon dioxide levels if you have a serious lung problem like asthma or chronic obstructive pulmonary disease ("COPD")

●To check the pH of your blood if you have symptoms of an acid-base disorder – Different medical problems, including some lung and kidney diseases, can cause the blood pH to get too high or too low. If you have a known acid-base disorder, an arterial blood gas test can be used to see how well treatment is working.

●If you have trouble breathing for reasons that are not clear

●If you have breathed in smoke, exhaust, or chemicals

●To check your oxygen and carbon dioxide levels during exercise

What happens during an arterial blood gas test? — For this test, you need to get a "blood draw." Often, this test is done while you are in the hospital. If not, your doctor or nurse will tell you where to go for the blood draw.

For the blood draw, a needle is used to take a small amount of blood from an artery. An artery in the wrist is most often used. But arteries in the upper arm, armpit, groin, or foot can also be used.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

For the test:

●If they are taking blood from an artery in your wrist, the staff might ask you to squeeze your hand into a fist. Then, they will press on your arteries before having you open your hand. This checks the blood flow to your hand.

●They will use a needle to take a small amount of blood from your artery. Collecting the blood only takes a few minutes.

●They will remove the needle, put pressure on the area with a piece of gauze, and bandage your arm.

●The blood will be sent to a lab for testing.

Most of the time, getting blood taken is very quick and does not cause problems. You might have some pain, bruising, or bleeding where the needle went in. Less commonly, a blood draw from an artery can cause problems with blood flow, a collection of blood under the skin, or dizziness. The medical staff will monitor you after your blood is taken to watch for any problems.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

The results of an arterial blood gas test include many different numbers. These include:

●Oxygen tension (PaO₂)

●Carbon dioxide tension (PaCO₂)

●Acidity (pH)

●Oxyhemoglobin saturation (SaO₂)

●Bicarbonate (HCO₃)

These numbers tell your doctor how much oxygen and carbon dioxide are in your blood. They also show how well these gases move through your bloodstream. The pH shows whether your blood has a normal balance of acids and bases.

If any of the results are abnormal, your doctor or nurse will talk to you about what to do next. They might need to do more tests to figure out the cause.

If you do have a health problem, your doctor will work with you to come up with a plan for treatment.

What else should I know? — If you are in the hospital and need to get arterial blood gas tests frequently, you might get an "arterial line" placed. This is similar to an IV, but goes into an artery instead of a vein. It lets the staff do the test without doing a blood draw.

More on this topic

Patient education: Breathing tests (The Basics)