Health Encyclopedia

CO2 test - serum

Definition

CO2 is carbon dioxide. A serum CO2 test measures the amount of carbon dioxide in the liquid part of your blood.

In the body, most of the CO2 is in the form of a substance called bicarbonate (HCO3-). Therefore, the CO2 blood test is really a measure of your bicarbonate level.

Alternative Names

Bicarbonate test; HCO3-; Carbon dioxide test; TCO2; Total CO2

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

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, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to prepare for the test

Your health care provider may tell you to stop taking any drugs that may affect test results. Corticosteroids and excessive use of antacids can increase bicarbonate levels.

How the test will feel

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.

Why the test is performed

The CO2 test is most often done as part of an electrolyte panel. Changes in your CO2 level suggest you may be losing or retaining fluid, cause an imbalance in your body's electrolytes. Electrolytes are minerals in your blood and other body fluids.

CO2 levels in the blood are influenced by kidney and lung function. The kidneys are mainly responsible for maintaining the normal bicarbonate levels.

Normal Values

The normal range is 20-29 mEq/L (milliequivalent per liter).

What abnormal results mean

Lower-than-normal levels may be due to:

Addison disease
Diarrhea
Ethylene glycol poisoning
Ketoacidosis
Kidney disease
Lactic acidosis
Metabolic acidosis
Methanol poisoning
Salicylate toxicity (such as aspirin overdose)

Higher-than-normal levels may be due to:

Breathing disorders
Cushing syndrome
Excessive vomiting
Hyperaldosteronism

The following conditions may also alter bicarbonate levels:

What the risks are

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.

Other risks associated with having blood drawn are slight but may include:

Excessive bleeding
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)

Review Date:5/17/2007
Reviewed By:Benjamin W. Van Voorhees, MD, MPH, Assistant Professor of Medicine, Pediatrics and Psychiatry, The University of Chicago, Chicago, IL. Review provided by VeriMed Healthcare Network.

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