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URL of this page: https://medlineplus.gov/lab-tests/carbon-dioxide-co2-in-blood/

Carbon Dioxide (CO2) in Blood

What is a Carbon Dioxide (CO2) Blood Test?

A carbon dioxide (CO2) blood test measures the amount of carbon dioxide in your blood. Carbon dioxide is an odorless, colorless gas. It is a waste product that your body makes when it uses food for energy.

Your blood carries carbon dioxide to your lungs. When you exhale, you breathe out carbon dioxide. Having too much or too little carbon dioxide in your blood can be a sign of a health problem.

Other names: carbon dioxide content, CO2 content, carbon dioxide blood test, bicarbonate blood test, bicarbonate test, total CO2; TCO2; carbon dioxide content; CO2 content; bicarb; HCO3

What is it used for?

Most of the carbon dioxide in your body is in the form of bicarbonate, which is a type of electrolyte. Electrolytes are electrically charged minerals that help control the amount of fluid and the balance of acids and bases (pH balance) in your body. A CO2 blood test is often part of a group of tests called an electrolyte panel.

An electrolyte panel may be part of a regular check-up. The test may also help diagnose or monitor conditions related to an electrolyte imbalance. These include high blood pressure and diseases of the kidneys, lungs, or liver.

Why do I need a CO2 in blood test?

Your health care provider may order a CO2 blood test as part of your regular checkup or if you have symptoms of an electrolyte imbalance. These symptoms may include:

Your provider may also order a CO2 blood test to check for side effects of certain medicines that can cause electrolyte imbalances.

What happens during a CO2 blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a CO2 blood test or an electrolyte panel. If your provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Abnormal test results may be a sign that your body is having a hard time keeping the right acid-base balance (pH balance). This may be because your lungs or kidneys are having a problem removing carbon dioxide or because you have an electrolyte imbalance. Many different types of conditions can cause these problems.

Too much CO2 in the blood can be a sign of many conditions, including:

Too little CO2 in the blood may be a sign of:

  • Addison disease, a complication of type 1 and type 2 diabetes
  • Diabetic ketoacidosis
  • Shock
  • Metabolic acidosis, a condition in which your blood is too acidic. It may be caused by many things, including kidney or liver disease, or long-lasting diarrhea.
  • Respiratory alkalosis, a condition in which your blood is not acidic enough because of lung or breathing disorders, including hyperventilation (rapid, deep breathing).

If your test results are not in the normal range, it doesn't necessarily mean you have a medical condition that needs treatment. Other factors, including certain medicines, can affect the level of CO2 in your blood. To learn what your results mean, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a CO2 blood test?

Some prescription and over-the-counter medicines can increase or decrease the amount of carbon dioxide in your blood. Be sure to tell your provider about any medicines you are taking.

References

  1. Hinkle J, Cheever K. Brunner & Suddarth's Handbook of Laboratory and Diagnostic Tests. 2nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Total Carbon Dioxide Content; p. 488.
  2. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co., Inc.; c2022. Addison Disease; [revised 2020 Oct; cited 2022 Feb 28]; [about 4 screens]. Available from: https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/adrenal-gland-disorders/addison-disease
  3. Merck Manuals [Internet]. Kenilworth (NJ): Merck & Co., Inc.; c2022. Consumer Version: Overview of Acid-Base Balance; [last full review 2021 Jul; cited 2022 Feb 4]; [about 3 screens]. Available from: https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance
  4. National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; NCI Dictionary of Cancer Terms: adrenal gland; [cited 2022 Feb 28]; [about 2 screens]. Available from: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/adrenal-gland
  5. National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; NCI Dictionary of Cancer Terms: carbon dioxide; [cited 2022 Feb 28]; [about 1 screens]. Available from: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/carbon-dioxide
  6. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests; [updated 2022 Mar 24; cited 2022 Feb 4]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/blood-tests
  7. Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Bicarbonate (Total CO2); [updated 2021 Nov 9; cited 2022 Feb 28]; [about 11 screens]. Available from: https://www.testing.com/tests/bicarbonate-total-co2/
  8. Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Cortisol; [updated 2021 Nov 9; cited 2022 Feb 28]; [about 16 screens]. Available from: https://www.testing.com/tests/cortisol/
  9. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Bicarbonate; [cited 2022 Feb 28]; [about 4 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=bicarbonate
  10. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Carbon Dioxide (Blood); [cited 2022 Feb 28]; [about 4 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=carbon_dioxide_blood

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.