A carbon dioxide (CO2) blood test measures the amount of carbon dioxide in your blood. Carbon dioxide is an odorless, colorless gas that is a waste product of metabolism. Most of the carbon dioxide in your body is in the form of bicarbonate, which is a type of electrolyte that helps control the amount of fluid and the balance of acids and bases (pH balance) in your body. A CO2 blood test is often part of a group of tests called an electrolyte panel, which helps healthcare providers determine if the body is balancing electrolytes properly.

During the test, a healthcare 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. The test usually takes less than five minutes. 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. Many different types of conditions can cause these problems.

The CO2 blood test results tell you whether the amount of carbon dioxide in your blood is within the typical range. A number higher or lower than the typical range may indicate a problem with your kidneys or lungs. If your number is too high or low, your provider will likely order more tests to confirm a diagnosis. In most cases, a CO2 blood test alone cannot diagnose a condition.