A carbon dioxide (CO2) blood test helps healthcare providers determine if the body is balancing electrolytes properly. Results outside the normal range of 20 to 29 millimoles per liter (mmol/L) may point to a more serious issue with the kidneys or lungs.
A CO2 blood test measures your level of bicarbonate, an indicator of how much CO2 is in your blood. CO2 is a form of natural waste that your body produces. Your blood carries CO2 to your lungs, where you breathe it out. Too little or too much CO2 in your blood may be a sign of a more serious health problem.
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A CO2 blood test is often done as part of an electrolyte panel (a type of blood test). Your healthcare provider may order a CO2 blood test if you have symptoms including:
Testing carbon dioxide levels in the blood helps healthcare providers see if your body is balancing electrolytes properly. Certain health conditions can cause electrolyte imbalances, including high blood pressure, kidney diseases and lung diseases.
A healthcare professional called a phlebotomist or phlebotomy technician usually performs the blood draw for the CO2 blood test. A medical laboratory technician runs the blood sample through a machine that determines the results.
Before the blood draw, ask your healthcare provider if you should stop taking any medications, vitamins or supplements. Sometimes, certain medications can affect the results of a blood test. Always ask your provider before stopping any medication.
You don’t need to stop eating or drinking (fast) before a CO2 blood test. But you may be having other blood tests in combination with a CO2 blood test that may require fasting. Ask your healthcare provider in advance if you should fast before the test.
For a CO2 blood test, the phlebotomist draws blood from a vein. The blood is drawn from the top of the hand or the inside of the elbow. You may feel a sharp prick as the needle enters the vein. The blood draw usually takes about a minute.
After collecting a blood sample, the phlebotomist removes the needle from the vein. They’ll apply light pressure to the blood draw location, then cover it with a bandage.
It usually takes a few days for CO2 blood test results to come back. Ask your healthcare provider how long you can expect to wait before getting your results.
Your CO2 blood test results come back with a number along with mmol/L. This is a measurement of carbon dioxide millimoles per liter of blood.
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.
A standard carbon dioxide level in the blood is anywhere from 20 to 29 mmol/L. Sometimes, this range varies slightly depending on the laboratory analyzing the blood test. Your healthcare provider will talk to you about your results and any next steps in your care.
When your blood has too much CO2, it means the body is not properly removing it (hypercapnia). Higher-than-normal CO2 levels in the blood could point to a health problem such as:
If you have a condition like COPD, oxygen therapy can sometimes balance carbon dioxide levels in the blood. Pulmonary rehabilitation and certain medications can help, too. If your CO2 levels are higher than normal, talk to your healthcare provider about the best treatment for you.
When your blood has lower-than-normal CO2, it means the body is removing too much CO2. Low CO2 levels in the blood is sometimes a sign of a health problem such as:
Some studies show that treatment with sodium bicarbonate or sodium citrate pills can help improve metabolic acidosis. Eating more fruits and vegetables (and fewer meats, eggs, cheese and cereal grains) can also help. Talk to your healthcare provider about the safest ways to balance the CO2 levels in your blood.
A note from Cleveland Clinic
If you experience fatigue, difficulty breathing, weakness, or excessive vomiting and diarrhea, your healthcare provider may order a CO2 blood test. This quick blood draw helps your provider see if the body is balancing electrolytes properly. Talk to your healthcare provider about any questions or concerns you may have.
Last reviewed by a Cleveland Clinic medical professional on 06/13/2022.
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