Health Encyclopedia

Carbon Dioxide (Blood)

Does this test have other names?


What is this test?

This test measures the amount of carbon dioxide in your blood.

When you digest food, your body makes carbon dioxide as a waste product in the form of gas. Your blood carries this gas to your lungs, where you exhale it and breathe in oxygen thousands of times a day. Normally, carbon dioxide in your bloodstream causes no problems, but if you have far too much or too little of it, you may have a disease or a medical emergency.

Most of the carbon dioxide in your body is in the form of bicarbonate, which is made by your kidneys. Bicarbonate is used to keep the acids and bases in your blood in balance.

The test measures all types of carbon dioxide in your blood – bicarbonate, carbonic acid, and dissolved CO2 – so it gives only an approximation of the bicarbonate concentration.

Why do I need this test?


You may also need this test if your doctor suspects that you have a lung, liver, or digestive disease. This is because your body uses carbon dioxide to maintain a healthy balance of acid-base, or pH, and electrolytes. These diseases are linked to altered blood bicarbonate levels.

You may also have this test if your doctor wants to check the progress of a disease linked to blood bicarbonate levels, such as Cushing syndrome. You may also have this test to look at any side effects of drugs like metformin that may lead to acidosis.

What other tests might I have along with this test?

Your doctor may also order an electrolyte panel, which measures your sodium, potassium, and chloride levels.

What do my test results mean?


Results are given in millimoles per liter (mmol/L). Normal values are 22 to 29 mmol/L in adults.

Higher levels of carbon dioxide may mean you have:

  • Metabolic alkalosis, or too much bicarbonate in your blood

  • Cushing syndrome

  • Hyperaldosteronism, an adrenal gland disorder

  • Kidney failure

Lower levels of carbon dioxide may mean you have:

  • Metabolic acidosis, or your blood overly acidic

  • Addison's disease, an adrenal gland disorder

  • Ketoacidosis

  • Lactic acidosis

How is this test done?


Does this test pose any risks?


What might affect my test results?

Certain medicines can affect your results.

How do I get ready for this test?


Medical Reviewers:

  • Bass, Pat F. III, MD, MPH
  • Stump-Sutliff, Kim, RN, MSN, AOCNS