Carbon Dioxide (CO2) in Blood Test
A carbon dioxide (CO2) blood test measures the amount of carbon dioxide in your blood. It helps check your body's acid-base balance and can detect problems with your lungs, kidneys, or metabolism.
What this test measures
This test measures the amount of carbon dioxide in your blood, mostly in the form of bicarbonate (HCO3), an electrolyte that helps control fluid levels and pH balance.
What your results mean
Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.
Higher-than-normal results
Too much CO2 in the blood (hypercapnia or hypercarbia) can be a sign of lung diseases, Cushing's syndrome, kidney failure, or metabolic alkalosis (blood not acidic enough).
Lower-than-normal results
Too little CO2 in the blood (hypocarbia) may be a sign of Addison disease, diabetic ketoacidosis, shock, or metabolic acidosis (blood too acidic).
Frequently asked questions
What is a CO2 blood test?
It measures the amount of carbon dioxide in your blood, mostly as bicarbonate, to check your body's acid-base balance.
Why is this test done?
It is often part of an electrolyte panel during a routine checkup or to help diagnose conditions related to electrolyte imbalance, such as high blood pressure or kidney, lung, or liver disease.
What does a high CO2 level mean?
A high level may indicate lung diseases, Cushing's syndrome, kidney failure, or metabolic alkalosis.
What does a low CO2 level mean?
A low level may indicate Addison disease, diabetic ketoacidosis, shock, or metabolic acidosis.
What should I do if my results are abnormal?
Abnormal results don't always mean you have a medical condition. Your provider may order other tests to confirm a diagnosis. Talk with your provider to understand your results.
Related lab tests
Sources
- MedlinePlus: Carbon Dioxide (CO2) in Blood — NIH MedlinePlus
Last updated . Information is aggregated from official public sources and is not a substitute for professional medical care.