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Also known as: HCO3-; Total CO2; TCO2
Formal name: Bicarbonate

Bicarbonate or total CO2 is different from the partial pressure of CO2 (PCO2).
To learn about PCO2 see blood gases.

At a Glance

Why Get Tested?

Usually as part of a renal profile (collection of tests which help investigate the kidney) to screen for an electrolyte or acid-base imbalance in conditions known to cause such disturbances, or to monitor a known imbalance

When to Get Tested?

May be part of a routine blood test that includes electrolyte measurements or may be requested by your doctor if you have a medical condition or are experiencing symptoms that could indicate problems with the acid-base balance of your body

Sample Required?

A blood sample drawn from a vein in the arm

Test Preparation Needed?


The Test Sample

What is being tested?

When you breathe, you bring oxygen (O2) into your lungs and release carbon dioxide (CO2). The bicarbonate test measures the total carbon dioxide in your blood [present in three forms: carbonic acid (H2CO3, CO2 dissolved in blood, and HCO3- (bicarbonate, the dominant form)]. HCO3- is an electrolyte that is excreted and reabsorbed by your kidneys. Its main job is to help maintain the acid-base balance (pH) in your body and secondarily to work with sodium, potassium and chloride to maintain electrical neutrality at the cellular level.

The bicarbonate test, since it measures all three forms at once, gives your doctor a rough estimation of acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood may be done if more information is needed. Bicarbonate may be measured along with sodium, potassium, and possibly chloride in an electrolyte profile as it is the balance of the three of four that gives your doctor the most information.

How is the sample collected for testing?

A blood sample is drawn by needle from a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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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.