Skip to content
My WebMD Sign In, Sign Up

Lung Disease & Respiratory Health Center

Font Size
A
A
A

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 slightly basic.
  • Bicarbonate (HCO3). Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.
  • 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 (O2).

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 to:

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 medicines.
  • 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?).

1 | 2 | 3 | 4

WebMD Medical Reference from Healthwise

Last Updated: May 30, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

Today on WebMD

Hot Tub Disease
Article
Lung Disease Health Check
HEALTH CHECK
 
Cigarette butts in ashtray
Article
Household Hazards For People With Copd
Article
 

Bronchitis Overview
SLIDESHOW
Copd Myth Fact Quiz
QUIZ
 
Living With Copd
VIDEO
Energy Boosting Foods
SLIDESHOW
 

cigarette butts snuffed out in ashtray
SLIDESHOW
Healthy Home Health Check
TOOL
 
Senior woman stretching
Article
Diagnosing Copd
VIDEO
 

WebMD Special Sections