Carbon Dioxide (CO2) in Blood

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 from metabolism, the process your body uses to make energy from food you eat.

Most of the carbon dioxide in your body is in the form of bicarbonate (HCO3), 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. Your blood carries carbon dioxide to your lungs, and then you breathe it out.

Too much or too little carbon dioxide in your blood can be a sign of a health problem.

Why this test is done

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

• Trouble breathing
• Confusion
• Weakness
• Fatigue
• Vomiting and/or diarrhea over a long period

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

How to prepare

Some prescription and over-the-counter medicines can increase or decrease the amount of carbon dioxide in your blood. You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

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.

Sample type

Blood

Other names for this test

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