An arterial blood gas (ABG) test measures the levels of oxygen and carbon dioxide in the blood to find out how well the lungs are working. An ABG test checks how well the lungs can move oxygen into the blood and remove carbon dioxide from the blood.

As blood passes through the lungs, oxygen moves into the blood while carbon dioxide moves out of the blood into the airspace of the lungs. An ABG test uses blood drawn from an artery, where the oxygen and carbon dioxide levels can be measured before they enter body tissues and become changed. An ABG test measures pH (acidity or alkalinity) and the levels of oxygen and carbon dioxide in the blood. Abnormal values for pH, oxygen, and carbon dioxide can be caused by changes in:

• Lung function.
• Heart function and blood flow.
• Kidney function.
• How well the body uses food for energy (metabolism).
• The use of some medicines.

An arterial blood gas test is often done for a person who is in the hospital because of severe injury or illness.