Bicarbonate (Total CO2)
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- Also Known As:
- Total CO2
- TCO2
- Carbon Dioxide Content
- CO2 Content
- Bicarb
- HCO3-

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At a Glance
Why Get Tested?
As part of an electrolyte panel or metabolic panel to identify or monitor an electrolyte imbalance or acid-base (pH) imbalance
When To Get Tested?
During a routine health exam or as recommended by your health care practitioner if you are experiencing symptoms such as weakness, confusion, prolonged vomiting, or breathing problems that could indicate an electrolyte imbalance or an acid-base imbalance (acidosis or alkalosis)
Sample Required?
A blood sample drawn from a vein
Test Preparation Needed?
None
What is being tested?
Bicarbonate is an electrolyte, a negatively charged ion that is used by the body to help maintain the body’s acid-base (pH) balance. It also works with the other electrolytes (sodium, potassium, and chloride) to maintain electrical neutrality at the cellular level. This test measures the total amount of carbon dioxide (CO2) in the blood, which occurs mostly in the form of bicarbonate (HCO3–). The CO2 is mainly a by-product of various metabolic processes.
Measuring bicarbonate as part of an electrolyte or metabolic panel may help diagnose an electrolyte imbalance or acidosis or alkalosis. Acidosis and alkalosis describe the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base). This imbalance is typically caused by some underlying condition or disease.
The lungs and kidneys are the major organs involved in regulating blood pH through the removal of excess bicarbonate.
- The lungs flush acid out of the body by exhaling CO2. Raising and lowering the respiratory rate alters the amount of CO2 that is breathed out, and this can affect blood pH within minutes.
- The kidneys eliminate acids in the urine and they regulate the concentration of bicarbonate (HCO3–, a base) in blood. Acid-base changes due to increases or decreases in HCO3– concentration occur more slowly than changes in CO2, taking hours or days.
Any disease or condition that affects the lungs, kidneys, metabolism, or breathing has the potential to cause acidosis or alkalosis.
The bicarbonate test gives a healthcare practitioner a rough estimate of your acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood (blood gases) may be done if more information is needed. Bicarbonate is typically measured along with sodium, potassium, and possibly chloride in an electrolyte panel as it is the balance of these molecules that gives the healthcare practitioner the most information.
Common Questions
View Sources
Sources Used in Current Review
2019 review by Patrick Sheehy, C(ASCP) and the Editorial Review Board.
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(May 17, 2002) Guidelines for Using Antiretroviral Agents Among HIV-Infected Adults and Adolescents. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5107a1.htm. Accessed on 07/02/2019.
(November 20, 2017) Metabolic Acidosis. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/000335.htm. Accessed on 07/15/2019.
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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.
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