CO2 blood test

Alternative Names: Bicarbonate test; HCO3-; Carbon dioxide test; TCO2; Total CO2; CO2 test - serum

CO2 is carbon dioxide. This article discusses the laboratory test to measures the amount of carbon dioxide in the liquid part of your blood, called the serum.

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 blood bicarbonate level.

See also: Blood gases

Why is the Test Performed?

The CO2 test is most often done as part of an electrolyte or basic metabolic panel. Changes in your CO2 level may suggest that you are losing or retaining fluid, which causes an imbalance in your body's electrolytes.

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

How is the Test Performed?

A blood sample is needed. For information on how this is done, see: Venipuncture

Preparation 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 will the Test 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.

CO2 blood test Risks

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)

Normal Results for CO2 blood test

The normal range is 23-29 mEq/L (milliequivalent per liter).

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

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
• Hyperaldosteronism
• Vomiting

The following conditions may also alter bicarbonate levels:

• Alkalosis
• Delirium
• Dementia
• Renal tubular acidosis; distal
• Renal tubular acidosis; proximal

Review Date: 5/30/2011
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

_{Do not use this information for medical emergencies - Call 911. This information should not be used for the diagnosis or treatment of any medical condition. A licensed medical practitioner should always be consulted for diagnosis and treatment of any and all medical conditions. Links to other websites do not constitute endorsements and are provided for information only. Any duplication or distribution of this information is strictly prohibited.
Copyright 2011 A.D.A.M., Inc.}