In arterial blood gases, the concentrations of various gases in the blood are measured. Arterial blood gas levels can provide important information about the respiratory function of the lungs and metabolic status. This test is used to analyze oxygen and carbon dioxide levels, as well as the acidity of the blood.

Oxygen is necessary for cellular function; it is inhaled and absorbed into the blood via the lungs. Abnormal levels may result from a variety of disorders, including nearly all forms of lung disease, anemia and oversedation from certain drugs.

Carbon dioxide (CO2) is a waste product of cellular metabolism that passes out of the blood in the lungs and is then exhaled. Carbon dioxide also acts as a buffer system to help maintain the acid-base balance of the blood. Abnormal levels can be caused by certain medications or by lung or kidney disease, severe vomiting, diabetic ketoacidosis (a life-threatening complication of type 1 diabetes mellitus), and other disorders.

pH levels give an indication of the acid-base balance of the blood. Abnormal levels can be caused by lung disease, kidney failure, severe vomiting or diarrhea, chronic heart failure, diabetic ketoacidosis, and other disorders.

Purpose of the Arterial Blood Gases

  • To evaluate how efficiently the lungs deliver oxygen to and remove carbon dioxide from the blood
  • To provide clues as to possible causes of shortness of breath
  • To determine the acidity of the blood
  • To monitor respiratory treatments, such as oxygen therapy or a ventilator

Who Performs Arterial Blood Gases

  • A doctor or a trained nurse or technician

Special Concerns about Arterial Blood Gases

  • This test requires drawing blood from an artery. Thus, it may cause more discomfort than most routine blood tests (which use blood from a vein), since arteries are deeper and have more nerves than veins.
  • This test should not be performed in people with severe bleeding disorders.

Before the Arterial Blood Gases

  • Report to your doctor any medications, herbs, or supplements that you regularly take. You may be advised to discontinue certain of these agents before the test.
  • If you are on oxygen therapy, your doctor will make sure that your oxygen concentration remains constant for 20 minutes before the test.

What You Experience

  • The person performing the test will select an artery in your arm, usually in the wrist, and check for adequate circulation by placing brief pressure on it, cutting off blood flow, and seeing how quickly color returns to the hand when the flow returns. If your palm does not turn pink within a few seconds, blood flow is insufficient, and the procedure will be repeated in your other arm. If blood flow is inadequate in both arms, an artery in your leg will be used.
  • Blood is drawn from the selected artery.

Risks and Complications of Arterial Blood Gases

  • Arterial puncture carries a significant risk that blood will collect and clot under the skin (hematoma) at the puncture site, causing swelling and discoloration. This is harmless but may cause some discomfort.
  • In rare cases, the puncture may damage the artery or nearby structures, such as a nerve.

After the Arterial Blood Gases

  • After the needle is removed, the person drawing blood will apply firm pressure on the puncture site for several minutes (or longer in patients who tend to bleed excessively, such as those who take anticoagulants or have a bleeding disorder).
  • A gauze bandage will then be firmly taped to the area.
  • If a large hematoma develops at the puncture site, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
  • Inform your doctor if you experience any pain, signs of infection (including fever and chills), weakness, numbness, tingling or bleeding in the limb used for the puncture.

Arterial Blood Gases Results

  • Your blood sample is analyzed in the office or is sent to a laboratory for analysis. The doctor will consider the test results together with your physical signs and symptoms.
  • Abnormal blood gas levels may indicate a wide variety of potential health problems. Additional tests, such as pulmonary function tests, are often necessary to establish a definitive diagnosis.
  • If lung function is severely reduced, the doctor may recommend treatment, such as oxygen therapy.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 05 Jan 2012

Last Modified: 11 Jul 2012