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, mostly in the form of bicarbonate. It is often part of an electrolyte panel and can help diagnose or monitor conditions related to an electrolyte imbalance, such as kidney, lung, or liver diseases.
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
Tell your provider about all medicines you take. You may need to stop certain medicines before the test. If your provider has ordered more tests on your blood sample, you may need to fast for several hours before the test. Follow your provider's instructions.
A health care professional will take a blood sample from a vein in your arm.
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
The test measures the amount of carbon dioxide in your blood, mostly in the form of bicarbonate. Abnormal levels may indicate an acid-base imbalance or electrolyte imbalance.
- High carbon dioxide level: High CO2 level (hypercapnia or hypercarbia) Limitation: High CO2 level (hypercapnia or hypercarbia) may be associated with lung diseases, Cushing's syndrome, kidney failure, metabolic alkalosis, or conditions that cause loss of acid such as vomiting, dehydration, and anorexia. Next step: Your provider may order other tests to confirm a diagnosis.
- Low carbon dioxide level: Low CO2 level (hypocarbia) Limitation: Low CO2 level (hypocarbia) may be associated with Addison disease, diabetic ketoacidosis, shock, metabolic acidosis, kidney or liver disease, long-lasting diarrhea, or respiratory alkalosis (e.g., from hyperventilation). 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
Your healthcare provider will interpret your CO2 blood test results, considering your symptoms, medical history, and other test results. Reference ranges may vary by laboratory. Do not self-diagnose.
- 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
U.S. National Library of Medicine: Carbon Dioxide (CO2) in Blood