Arterial Blood Gas (ABG) Test

What is arterial blood gas?

An arterial blood gas test is one of the tests used for COPD diagnosis. The test measures the oxygen (O2) level in your blood and if carbon dioxide (CO2) is removed properly. It can also determine the acidity (pH) of your blood. Imbalances in the amount of oxygen, carbon dioxide, or pH can serve as a way to evaluate respiratory diseases, kidney function, and the body’s metabolism (the process by which our body converts food into energy that can be used right away or stored in the liver, muscles and body fat). Results of the test can show the severity of COPD and whether a person needs oxygen therapy.

How to prepare

There is no need to do any special preparation for this test. However, if you are on oxygen therapy, oxygen values must be constant for 20 minutes before the test.

If you are taking medication to make your blood thinner or aspirin, you should tell your doctor beforehand.

How it is done

Our diaphragm, lungs, bones and muscles contract and expand when we breathe. When we breathe in, we inhale oxygen from the air and when we breathe out, we exhale carbon dioxide, a waste gas that results from our body’s processes.

Arterial blood transports oxygen to all parts of our body. This type of blood is used in the blood gas analysis test. To collect the blood, a needle is inserted into an artery, usually in the wrist, and the blood is immediately sent to the laboratory for accurate results.

What is the normal range for blood gases?

The main measurements from the arterial blood gas test include:

  • The level of hydrogen ions (H+) in the blood. Normal values are between 7.38 and 7.42. The acidity or alkalinity of the blood is linked with the amount of carbon dioxide in the blood. Acidic blood (pH less than 7.38) has high carbon dioxide levels in the blood. Alkaline blood (pH greater than 7.42) has low carbon dioxide levels in the blood.
  • Partial pressure of oxygen (PaO2). This is the amount of oxygen gas dissolved in the test. Values below 75 to 100 mm Hg (blood pressure is measured in millimeters of mercury) show that carbon dioxide levels in the blood are high and pH is acidic (less than 7.38).
  • Partial pressure of carbon dioxide (PaCO2). This is the amount of carbon dioxide in the blood. If PaCO2 levels are above normal values (38 to 42 mm Hg), blood is more acidic (pH less than 7.38). PaCO2 levels below normal values mean that the blood is alkaline.

Results from any of these parameters can reveal lung, kidney or metabolic conditions. In COPD, the blood is more acidic, as the pH levels are low and the PaCO2 levels are above normal.

Side effects and warnings

The arterial blood gas test is safe. Taking blood from some people may be more difficult than others, as veins and arteries vary in size.

During the test you may feel brief pain. Arteries pump blood, so it may take a while before you stop bleeding. The bleeding can take more time to stop if you are taking aspirin or medicines that make your blood thinner.

Other side effects may include, bruising, hematoma, fainting or feeling light-headed, and infection.

Other details

pH levels can reveal more information on your metabolism, including diabetes or kidney function.

An arterial blood test may be done on people with head or neck trauma as their injuries may affect breathing. During cardiac bypass or brain surgery, this test may be used to monitor blood gases during and after the procedure.


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