Carbon Dioxide (CO2) in Blood

What is a carbon dioxide (CO2) blood test?

Carbon dioxide (CO2) is an odorless, colorless gas. It is a waste product made by your body. Your blood carries carbon dioxide to your lungs. You breathe out carbon dioxide and breathe in oxygen all day, every day, without thinking about it. A CO2 blood test measures the amount of carbon dioxide in your blood. Too much or too little carbon dioxide in the blood can indicate a health problem.

Other names: carbon dioxide content, CO2 content, carbon dioxide blood test, bicarbonate blood test, bicarbonate test, total CO2; TCO2; carbon dioxide content; CO2 content; bicarb; HCO3

What is it used for?

A CO2 blood test is often part of a series of tests called an electrolyte panel. Electrolytes help balance the levels of acids and bases in your body. Most of the carbon dioxide in your body is in the form of bicarbonate, which is a type of electrolyte. An electrolyte panel may part of a regular exam. The test may also help monitor or diagnose conditions related to an electrolyte imbalance. These include kidney diseases, lung diseases, and high blood pressure.

Why do I need a CO2 in blood test?

Your health care provider may have ordered a CO2 blood test as part of your regular checkup or if you have symptoms of an electrolyte imbalance. These include:

  • Difficulty breathing
  • Weakness
  • Fatigue
  • Prolonged vomiting and/or diarrhea

What happens during a CO2 blood 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. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don’t need any special preparations for a CO2 blood test or an electrolyte panel. If your health care provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

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.

What do the results mean?

Abnormal results may indicate that your body has an electrolyte imbalance, or that there is a problem removing carbon dioxide through your lungs. Too much CO2 in the blood can indicate a variety of conditions including:

  • Lung diseases
  • Cushing’s syndrome, a disorder of the adrenal glands. Your adrenal glands are located above your kidneys. They help control heart rate, blood pressure, and other body functions. In Cushing’s syndrome, these glands make too much of a hormone called cortisol. It causes a variety of symptoms, including muscle weakness, vision problems, and high blood pressure.
  • Hormonal disorders
  • Kidney disorders
  • Alkalosis, a condition in which you have too much base in your blood

Too little CO2 in the blood may indicate:

  • Addison’s disease, another disorder of the adrenal glands. In Addison’s disease, the glands don’t produce enough of certain types of hormones, including cortisol. The condition can cause a variety of symptoms, including weakness, dizziness, weight loss, and dehydration.
  • Acidosis, a condition in which you have too much acid in your blood
  • Ketoacidosis, a complication of type 1 and type 2 diabetes
  • Shock
  • Kidney disorders

If your test results are not in the normal range, it doesn’t necessarily mean you have a medical condition requiring treatment. Other factors, including certain medicines, can affect the level of CO2 in your blood. To learn what your results mean, talk to your health care provider.

Is there anything else I need to know about a CO2 blood test?

Some prescription and over-the-counter medicines can increase or decrease the amount of carbon dioxide in your blood. Be sure to tell your health care provider about any medicines you are taking.

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