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Alternative names
Bicarbonate test; HCO3-; Carbon dioxideDefinition Return to top
This 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-.
How the test is performed Return to top
Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill 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.
Infant or young child, 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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
CO2 and bicarbonate are also measured as part of an arterial blood gas analysis.
How to prepare for the test Return to top
The health care provider may advise you to discontinue drugs that may affect the test (see "Special Considerations").How the test will feel Return to top
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.Why the test is performed Return to top
The CO2 levels in the blood are influenced by kidney and respiratory (lung) function.Normal Values Return to top
The normal range is 20-29 mEq/L (milliequivalent per liter)What abnormal results mean Return to top
Lower-than-normal levels of HCO3- may indicate:What the risks are Return to top
Special considerations Return to top
Drugs that can increase HCO3- measurements include corticosteroids and excessive use of antacids.
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Page last updated: 28 October 2004 |