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Carbon Dioxide (Bicarbonate)

Test Overview

Carbon dioxide (CO2) is a gaseous waste product from metabolism. The blood carries carbon dioxide to your lungs, where it is exhaled. More than 90% of carbon dioxide in your blood exists in the form of bicarbonate (HCO3). The rest of the carbon dioxide is either dissolved carbon dioxide gas (CO2) or carbonic acid (H2CO3). Your kidneys and lungs balance the levels of carbon dioxide, bicarbonate, and carbonic acid in the blood.

This test measures the level of bicarbonate in a sample of blood from a vein. Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.

Bicarbonate is not usually tested by itself. It may be done on a blood sample taken from a vein as part of a panel of tests that looks at other electrolytes, such as sodium, potassium, and chloride. It can also be done as part of an arterial blood gas (ABG) test. For the arterial blood gas study, the blood sample is taken from an artery.

Why It Is Done

A carbon dioxide (bicarbonate) test helps find and keeps track of conditions that affect blood bicarbonate levels, including many kidney diseases, some lung diseases, and metabolic conditions.

It is often done as part of a group of laboratory blood tests (chemistry screen) to help find the cause of many kinds of symptoms.

How To Prepare

You do not need to do anything before you have this test.

Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

The health professional drawing blood will:

  • Wrap an elastic band around your arm to stop the flow of blood.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Apply a gauze pad or cotton ball over the needle site as the needle is removed.
  • Apply pressure to the site and then a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

There is very little risk of complications from having blood drawn from a vein.

  • You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.
  • In rare cases, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your health professional before your blood is drawn.

Results

A carbon dioxide (bicarbonate) test measures the level of bicarbonate in the blood.

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are usually available in 1 to 2 days.

Carbon dioxide (bicarbonate)
Normal:

23–30 mEq/L (23–30 mmol/L)

High values

High carbon dioxide (bicarbonate) levels may be caused by:

Low values

Low carbon dioxide (bicarbonate) levels may be caused by:

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include the following:

  • You drink liquids that are very acidic, such as orange juice or some types of carbonated beverages, shortly before having the test.
  • You are taking some medicines, such as diuretics, some antibiotics, glaucoma medicine, and corticosteroids.
  • The health professional leaves on the elastic band that stops blood flow for an extended amount of time before the blood sample is collected.

What To Think About

  • The carbon dioxide (bicarbonate) test also can be done on a blood sample taken from an artery for an arterial blood gas (ABG) test. For more information, see the topic Arterial Blood Gases.

References

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Credits

By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Robert L. Cowie, MB, FCP(SA), MD, MSc, MFOM - Pulmonology
Last Revised June 14, 2010

Last Revised: June 14, 2010

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Robert L. Cowie, MB, FCP(SA), MD, MSc, MFOM - Pulmonology

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