Carbon Dioxide (CO2) in Blood
Reviewed
Also called: carbon dioxide content, CO2 content, carbon dioxide blood test, bicarbonate blood test, bicarbonate test, total CO2 TCO2 bicarb HCO3
A carbon dioxide (CO2) blood test measures the amount of carbon dioxide in your blood. Too much or too little carbon dioxide in your blood can be a sign of a health problem.
Specimen: Blood from a vein
Why this test may be ordered
- As part of a routine checkup
- If you have symptoms of an electrolyte imbalance, such as trouble breathing, confusion, weakness, fatigue, or prolonged vomiting/diarrhea
- To check for side effects of certain medicines that can cause electrolyte imbalances
Preparation and collection
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.
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. This usually takes less than five minutes.
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.
Understanding results
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.
- High carbon dioxide level (hypercapnia): Too much CO2 in the blood (called hypercapnia or hypercarbia) can be a sign of many conditions, including: Lung diseases. Metabolic alkalosis, a condition in which your blood is not acidic enough. Limitation: If your test results are not in the normal range, it doesn't necessarily mean you have a medical condition that needs treatment. Next step: Your provider may order other tests to confirm a diagnosis.
- Low carbon dioxide level (hypocarbia): Too little CO2 in the blood (hypocarbia) may be a sign of: Addison disease. Diabetic ketoacidosis, a complication of type 1 and type 2 diabetes. Metabolic acidosis, a condition in which your blood is too acidic. Respiratory alkalosis, a condition in which your blood is not acidic enough because of a lung or breathing problem, including hyperventilation (rapid, deep breathing). Limitation: Other factors, including certain medicines, can affect the level of CO2 in your blood. Next step: Your provider may order other tests to confirm a diagnosis.
- Results may be affected by certain prescription and over-the-counter medicines.
- An abnormal result does not necessarily mean you have a condition that needs treatment; your provider will order other tests to confirm a diagnosis.
What to do next
To learn what your results mean, talk with your provider.
- What is a carbon dioxide (CO2) blood test?
- What is it used for?
- Why do I need a CO2 in blood test?
- What happens during a CO2 blood test?
- Will I need to do anything to prepare for the test? Are there any risks to the test? What do the results mean? Is there anything else I need to know about a CO2 blood test?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Carbon Dioxide (CO2) in Blood