An arterial blood gas (ABG) study is a blood test that measures the levels of different gases in the blood, including oxygen and carbon dioxide. Because the test requires oxygen-rich blood, the blood sample must be taken from an artery rather than a vein. Some people find this method of drawing blood to be more painful than the standard method.

Many diseases cause similar symptoms, such as chest pain, dizziness, shortness of breath, hypoventilation (slow, shallow breathing) or hyperventilation (rapid, deep breathing). The ABG can help a physician determine whether those symptoms are caused by metabolic, respiratory or other conditions. The test is also used to assess how well a patient’s lungs are functioning after they have been on a heart-lung machine during open-heart surgery. Furthermore, the test may be ordered for patients who are undergoing respiratory therapy or who are on a ventilator (a machine that breathes for the patient), and to assess how well the kidneys are functioning.