Total CO2 or bicarbonate is different than the partial pressure of CO2 (PCO2). Learn about PCO2
At a Glance
Why Get Tested?
When to Get Tested?
During a routine physical or as recommended by your doctor if you are experiencing symptoms such as weakness, confusion, prolonged vomiting, or respiratory distress that could indicate an electrolyte imbalance or acidosis or alkalosis
A blood sample drawn from a vein in the arm
Test Preparation Needed?
The Test Sample
What is being tested?
The total CO2 test measures the total amount of carbon dioxide in the blood, which occurs mostly in the form of bicarbonate (HCO3-). Bicarbonate is a negatively charged ion 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.
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.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Pagana and Pagana. Mosby’s Manual of Diagnostic and Laboratory Tests. Fourth Edition. Pp 152-154.
MedlinePlus Medical Encyclopedia. CO2 blood test. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003469.htm. Accessed September 2011.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
(1995-2004). Minerals and Electrolytes. The Merck Manual of Medical Information – Second Home Edition [On-line information]. Available online at http://www.merck.com/mmhe/sec12/ch155/ch155a.html?qt=electrolytes&alt=sh through http://www.merck.com.
Ben-Joseph, E., Reviewed (2004 July). Dehydration. Familydoctor.org Information for Parents [On-line information]. Available online at http://www.kidshealth.org/PageManager.jsp?dn=familydoctor&lic=44&article_set=21646 through http://www.kidshealth.org.
Webner, D., Updated (2003 August 18). CO2. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003469.htm.
A.D.A.M. editorial, Updated (2003 October 15). Electrolytes. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/002350.htm.
Voorhees, B (Updated May 17, 2007). MedlinePlus Medical Encyclopedia: CO2 test, serum. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003469.htm. Accessed July 2008.
Clarke, W and Dufour D R, Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp 321-322.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006. Pp 157-159.