Blood gases

Blood Gases

Blood gases are a type of laboratory tests that measure how well your lungs are functioning and how much oxygen is in your blood. They are often ordered for people who have conditions such as chronic obstructive pulmonary disease (COPD), asthma, pneumonia, and other lung or heart diseases. They can also be used to find out the oxygen levels in people who are having difficulty breathing, are on ventilators, or have had a respiratory arrest.


Most of the time, no special preparation is needed for blood gas testing. However, for the most accurate results, your doctor may ask you to stop smoking or limit physical activity before the test. Additionally, you may be asked to remove any piercings and jewelry from your arms during the test.


Blood gases are most commonly performed using a peripheral venipuncture—the same technique used for drawing blood for other tests. A small sample of your blood is drawn from either the radial artery in your wrist, your cubital vein in your elbow, or a vein near the collarbone. Once the sample has been drawn, it’s placed into a special container and sent to a laboratory for testing.


There are several types of blood gas tests, including partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), arterial oxygen saturation (SaO2), and bicarbonate (in whole blood). Some tests measure only one of these components, while others measure more than one.


Blood gas testing is a safe procedure with very few risks. The most common complication is a slight bruise at the site where the needle is inserted. Additionally, the artery in your wrist can sometimes be difficult to find, which may cause some discomfort.

Why it's done

Blood gas tests are done to measure the levels of oxygen and carbon dioxide in your blood. Additionally, tests that measure pH levels in the blood can help diagnose and monitor conditions such as lung or heart disease. These tests can also help assess the effectiveness of treatments.

When it's done

Blood gases may be ordered when a person is having difficulty breathing or is on a ventilator. These tests can also be used to check for conditions such as asthma, COPD, or pneumonia. Additionally, blood gases may be used to assess the need for oxygen therapy or to monitor the effectiveness of current treatments.