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CO2
Also known as: Total CO2, TCO2, Bicarbonate Formal name: Carbon Dioxide Content Related tests: Electrolyte panel, sodium, potassium, chloride
Total CO2 or bicarbonate is different than the partial pressure of CO2 (PCO2). To learn about PCO2, click here.
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The Test Sample
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What is being tested?The CO2 test measures the total amount of carbon dioxide in the blood, mostly in the form of bicarbonate (HCO3-). Bicarbonate is a negatively charged electrolyte that is excreted and reabsorbed by the kidneys. It is used by the body to help maintain the body’s acid-base balance (pH) and secondarily to work with sodium, potassium, and chloride to maintain electrical neutrality at the cellular level. Since the CO2 test measures all three forms of carbon dioxide in the blood (bicarbonate, H2CO3 [also known as carbonic acid], and dissolved CO2) as a total CO2, it will give a rough estimate but not an exact determination of the bicarbonate concentration.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
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This article was last reviewed on
April 22, 2005.
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