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Home Knowledge Center Wellness Library Carbon Dioxide (CO2) Test

Carbon Dioxide (CO2) Test

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 it in your blood exists in the form of bicarbonate (HCO3). The rest of it 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 that acts as a buffer. It keeps the pH of blood from becoming too acidic or too basic.

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

Why It Is Done

Why It Is Done

CO2 testing is often done as part of a group of blood tests (chemistry screen) to help find the cause of many kinds of symptoms. These causes may include many kidney diseases, some lung diseases, and metabolic problems.

How To Prepare

How To Prepare

  • In general, there's nothing you have to do before this test, unless your doctor tells you to.
  • Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may affect the results of the test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
How It Is Done

How It Is Done

  • A health professional uses a needle to take a blood sample, usually from the arm.

How long the test takes

The test will take a few minutes.

How It Feels

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

Results

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

Results are usually ready in 1 to 2 days.

High values

A high level may be caused by:

  • Vomiting.
  • Dehydration.
  • Blood transfusions.
  • Overuse of medicines that contain bicarbonate (especially antacids).
  • Conditions such as anorexia, chronic obstructive pulmonary disease (COPD), fluid in the lungs (pulmonary edema), heart disease, Cushing's disease, or Conn's syndrome.

Low values

A low level may be caused by:

  • Hyperventilation.
  • Aspirin or alcohol overdose.
  • Diarrhea, dehydration, or severe malnutrition.
  • Liver or kidney disease.
  • A massive heart attack.
  • Hyperthyroidism or uncontrolled diabetes.
  • A serious infection of the whole body (sepsis).

This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Learn how we develop our content.

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Related Links

Medical Tests: Questions to Ask the Doctor

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