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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
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.
How to prepare for the testThe health care provider may advise you to discontinue drugs that may affect the test (see "Special Considerations").
For infants and children:
The preparation you can provide for this test depends on your child's age and previous experience. For specific information regarding how you can prepare your child, see the following topics:
How the test will feelWhen 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 performedThe CO2 levels in the blood are influenced by kidney and respiratory (lung) function.
Normal ValuesThe normal range is 20-29 mEq/L (milliequivalent per liter)
What abnormal results meanLower-than-normal levels of HCO3- may indicate:
Additional conditions under which the test may be performed:
What the risks are
Special considerationsDrugs that can increase HCO3- measurements include corticosteroids and excessive use of antacids.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Update Date: 8/18/2003David Webner, M.D., Sports Medicine Fellow, Crozer-Keystone Family Practice Program, Springfield, PA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT