Arterial Blood Gas (ABG) Test

Why this test may be ordered

• To help diagnose serious problems with your lungs and breathing (how well they move oxygen into the blood and remove carbon dioxide).
• To help diagnose kidney disorders that affect pH balance.
• To find out whether treatment for breathing disorders, kidney disease, or conditions affecting acid-base balance is working.

Preparation and collection

Tell your provider about all the medicines and supplements you take. Do not stop any medicine unless your provider tells you to. If you take blood thinners (including aspirin), ask your provider whether you should stop them before the test. If you are on oxygen therapy, your oxygen may be turned off for about 20 minutes before the test, but only if you can breathe without it.

A health care provider takes a blood sample from an artery (often inside the wrist, but may be from your arm or groin). For a newborn, the sample may be taken from the heel or umbilical cord. The provider first checks blood circulation in your wrist, then may apply numbing medicine. After inserting a needle and syringe to remove blood, pressure is applied for at least 5 minutes to stop bleeding.

There is very little risk to having an arterial blood gas test. You may have some bleeding, bruising, or soreness at the spot where the needle was put in. Very rarely, the needle may damage a nerve or the artery. You may be told to avoid lifting heavy objects for 24 hours after the test.

Understanding results

ABG test results involve many body systems that affect each other. Many health conditions can cause abnormal results. It is best to have your provider explain what your results mean for your health.

• Oxygen saturation (O2Sat): 95-100%: Abnormal results may mean a problem with your lungs or kidneys or a metabolic disorder. Limitation: An ABG test alone usually cannot provide a diagnosis. Next step: If not normal, your provider will likely order more tests.
• Partial pressure of oxygen (PaO2): 75-100 mmHg: Abnormal results may mean a problem with your lungs or kidneys or a metabolic disorder. Limitation: An ABG test alone usually cannot provide a diagnosis. Next step: If not normal, your provider will likely order more tests.
• Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg: Abnormal results may mean a problem with your lungs or kidneys or a metabolic disorder. Limitation: An ABG test alone usually cannot provide a diagnosis. Next step: If not normal, your provider will likely order more tests.
• Acid-base balance (pH level): 7.35-7.45: Abnormal results may mean a problem with your lungs or kidneys or a metabolic disorder. Extremely abnormal pH can affect many organs and become life-threatening. Limitation: An ABG test alone usually cannot provide a diagnosis. Next step: If not normal, your provider will likely order more tests.

• Arterial puncture is more uncomfortable than a blood draw from a vein.
• You may have some bleeding, bruising, or soreness at the puncture site.
• Very rarely, the needle may damage a nerve or the artery.
• You may be told to avoid lifting heavy objects for 24 hours after the test.
• An ABG test alone usually cannot provide a diagnosis; your provider will likely order more tests if results are not normal.

What to do next

Your provider will explain what your results mean for your health. Abnormal results may lead to additional tests for your lungs, kidneys, or for metabolic disorders.

• What do my ABG results mean for my breathing, kidney function, and acid-base balance?
• Will I need follow-up tests based on these results?
• Do I need to adjust my oxygen therapy before the test?
• Should I stop taking any medicines (including blood thinners or aspirin) beforehand?

Evidence source

U.S. National Library of Medicine: Arterial Blood Gas (ABG) Test