What is carbon dioxide (CO2) blood test?

Carbon dioxide blood test

Carbon dioxide (CO2) is a gas without odor or color. It is a waste product produced by the body. Blood transports carbon dioxide from the body to the lungs. You inhale oxygen and exhale carbon dioxide all day, daily, without thinking. The CO2 analysis in blood measures the amount of carbon dioxide present in the blood. A lot or little carbon dioxide in the blood could indicate a health problem.

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

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For what do you use it?

CO2 analysis is usually part of a series of electrolyte tests called ionograms. Electrolytes help balance the levels of acids and bases in the body. Most of the carbon dioxide in the body is in the form of bicarbonate, a type of electrolyte. The ionogram can be part of a routine examination. This test also allows to monitor or diagnose problems related to an electrolyte imbalance, for example, diseases of the kidneys, lungs or high blood pressure (hypertension).

Why do I need a CO2 blood test?

Your doctor or health professional can order a blood CO2 test as part of routine monitoring or if you have symptoms of an electrolyte imbalance, for example:

  • Difficulty breathing
  • Weakness
  • Fatigue
  • Prolonged vomiting or diarrhea

What happens during a CO2 blood test?

A health professional takes a blood sample from a vein in an arm with a small needle. After inserting the needle, remove a small amount of blood that is placed in a test tube or vial. You may feel mild discomfort when the needle is inserted or removed. This usually takes less than five minutes.

Will I have to do something to prepare for the test?

The analysis of CO2 in blood and the ionogram does not require any special preparation. If your doctor or health professional has ordered other tests with your blood sample, you may have to fast (not eat or drink) for several hours before the test. Your doctor or health professional will tell you if you need to follow any special instructions.



Does this test have any risk?

The risks of a blood test are minimal. You may feel mild pain or a bruise where the needle is inserted, but most symptoms disappear quickly.

What do the results mean?

Abnormal results may indicate that your body has an electrolyte imbalance or a problem removing carbon dioxide from the lungs. An excess of CO2 in the blood could indicate problems such as:

  • Lung disease
  • Diseases of the adrenal glands. The adrenal glands are on top of the kidneys and control heart rate, blood pressure, and other body functions
  • Hormonal problems
  • Diseases of the kidneys
  • Alkalosis, an excess of the base (alkalinity) in the blood

An insufficient amount of CO2 in the blood can indicate:

  • Addison's disease, in which the adrenal glands do not produce enough of certain types of hormones. This can cause a variety of symptoms, for example, weakness, dizziness, weight loss and dehydration
  • Acidosis, an excess of acid in the blood
  • Ketoacidosis, a complication of type 1 and type 2 diabetes
  • Shock
  • Diseases of the kidneys

If your results are not within normal limits, that does not necessarily mean that you have a medical problem that requires treatment. There are other factors, such as certain medications, that can affect the levels of CO2 in the blood. To understand the meaning of your results, check with your doctor or health professional.

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

Some prescription and over-the-counter (OTC) medications can increase or decrease the amount of carbon dioxide in the blood. Tell your doctor or health professional about the medicines you take.