CO2

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Serum CO2 is a blood test that measures the amount of carbon dioxide (CO2) in serum (the liquid portion of the blood).

Serum CO2 is really a measure of serum HCO3-, also called bicarbonate. The procedure used to measure HCO3- in the laboratory first converts it to CO2. In the body, 95% of the CO2 is present as HCO3-, so most of what is measured in the laboratory represents HCO3-.

Bicarbonate test; HCO3-; Carbon dioxide

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

CO2 and bicarbonate are also measured as part of an arterial blood gas analysis.

The health care provider may advise you to discontinue drugs that may affect the test.

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

The CO2 levels in the blood are influenced by kidney and respiratory (lung) function.

Review Date: 06/03/2005
Reviewed By: Thomas A. Owens, M.D., Departments of Internal Medicine and Pediatrics, Duke University Medical Center, Durham, NC. Review provided by VeriMed Healthcare Network.