Arterial Blood Gases
An arterial blood gas (ABG) test measures the
acidity (pH) and the levels of oxygen and carbon dioxide in the
blood from an artery. This test is used to check how well your lungs are able
to move oxygen into the blood and remove carbon dioxide from the blood.
As blood passes through your lungs, oxygen moves into the blood while
carbon dioxide moves out of the blood into 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. An ABG measures:
- Partial pressure of oxygen (PaO2). This measures
the pressure of oxygen dissolved in the blood and how well oxygen is able to
move from the airspace of the lungs into the blood.
- Partial pressure of carbon dioxide (PaCO2). This
measures the pressure of carbon dioxide dissolved in the blood and how well carbon
dioxide is able to move out of the body.
- pH. The pH measures hydrogen ions (H+) in blood.
The pH of blood is usually between 7.35 and 7.45. A pH of less than 7.0 is
called acid and a pH greater than 7.0 is called basic (alkaline). So blood is
- Bicarbonate (HCO3). Bicarbonate is a chemical
(buffer) that keeps the pH of blood from becoming too acidic or too
- Oxygen content (O2CT) and oxygen saturation (O2Sat) values. O2 content measures the amount of oxygen in the blood.
Oxygen saturation measures how much of the
hemoglobin in the red blood cells is carrying oxygen
Blood for an ABG test is taken from an artery. Most
other blood tests are done on a sample of blood taken from a vein, after the
blood has already passed through the body's tissues where the oxygen is used up
and carbon dioxide is produced.
Why It Is Done
An arterial blood gas (ABG) test is done
How To Prepare
Tell your doctor if you:
- Have had bleeding problems or take blood thinners, such as
aspirin or warfarin (Coumadin).
- Are taking any
- Are allergic to any medicines, such as those used to
numb the skin (anesthetics).
If you are on oxygen therapy, the oxygen may be turned off
for 20 minutes before the blood test. This is called a "room air" test. If you
can't breathe without the oxygen, the oxygen will not be turned off.
Talk to your doctor about any concerns you have regarding the need for
the test, its risks, how it will be done, or what the results may mean. To help
you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).