Blood gases is a measurement of how much oxygen and carbon dioxide is in your blood. It also determines the acidity (pH) of your blood.

The test is used to evaluate respiratory diseases and conditions that affect the lungs. It helps determine the effectiveness of oxygen therapy. The test also provides information about the body's acid/base balance, which can reveal important clues about lung and kidney function and the body's general metabolic state.

See also:

• Acidosis
• Diabetic ketoacidosis
• Lactic acidosis
• Metabolic acidosis
• Respiratory acidosis
• Respiratory alkalosis

Usually, blood is taken from an artery. The blood may be collected from the radial artery in the wrist, the femoral artery in the groin, or the brachial artery in the arm.

The health care provider may test circulation to the hand before taking a sample of blood from the wrist area.

The health care provider will insert a small needle through the skin into the artery. You can choose to have numbing medicine (anesthesia) applied to the site before the test begins.

In rare cases, blood from a vein may be used.

After the blood is taken, pressure is applied to the site for a few minutes to stop the bleeding. The health care provider will watch the site for signs of bleeding or circulation problems.

The sample must be quickly sent to a laboratory for analysis to ensure accurate results.

There is no special preparation. If you are on oxygen therapy, the oxygen concentration must remain constant for 20 minutes before the test.

You may feel brief cramping or throbbing at the puncture site.