CO2 Blood Test to Check Carbon Dioxide Levels

Carbon dioxide (CO2) blood tests evaluate the presence of the gas in your blood. If your CO2 levels rise too high or fall too low, the test results may be an indication that you have a health condition that needs diagnosis and treatment.

Your body produces CO2 gas as a byproduct. It's carried by the bloodstream to your lungs, primarily in a bicarbonate (HCO3) form, and then exhaled out while breathing. In a healthy individual, the presence of CO2 in the blood stays within a normal range and doesn’t present any problems.

This article explains why your healthcare provider might order a carbon dioxide blood test and the types of diseases and disorders the results may suggest. It offers a step-by-step approach covering what to expect during a carbon dioxide blood test.

A Word From Verywell

Your CO2 can be affected by underlying conditions or even everyday activities, like eating, hydration, and alcohol, which can lead to an imbalance in your body. In addition, conditions that affect the respiratory system, renal system, and endocrine system also play a role in CO2 balance. This article helps advise on what you can do to protect your health and CO2 balance.

Purpose of the Test

Typically, a CO2 blood test is done in conjunction with an electrolyte panel, which measures sodium, potassium, and chloride levels, or as part of a metabolic panel. Electrolytes are an integral part of the way your body regulates its fluid balance and maintains appropriate acid-base (pH) levels. A CO2 blood test evaluates whether your body is balancing electrolytes correctly.

Additionally, your healthcare provider may use this test to monitor other health conditions, such as those that affect the kidneys, liver, blood pressure, and more. It may also be a helpful test in monitoring the effects of some medications.

Bicarbonate (HCO3) serves a vital purpose in your blood—it helps keep the body’s acids and bases in check. The purpose of the carbon dioxide (CO2) blood test is to confirm whether or not there’s a fluctuation in your CO2 levels and an electrolyte imbalance in your body.

Sometimes it is useful to measure the amount of carbon dioxide in the arteries along with the HCO3 in your veins. This is most often helpful in people with a lung disorder, used to determine how well the lungs are functioning. It's called an arterial blood gases (ABG) test and the blood is taken from an artery rather than a vein.

A carbon dioxide blood test may be known as other names, including:

• Carbon dioxide content
• CO2 content
• Bicarbonate blood test
• Bicarbonate test
• Total CO2
• TCO2
• HCO3
• CO2 test-serum

Some of these tests can be performed on both arterial and venous blood, while others can only be performed on one or the other.

Risks and Contraindications

The carbon dioxide blood test should be similar to any blood tests you’ve had done in the past. You may feel some pain or have minor bruising afterward but, in general, the risks and contraindications are minimal.

Be sure to tell your healthcare provider about any medications you’re taking, even over-the-counter ones. Drugs like corticosteroids or antacids can skew the lab results, and your practitioner will want to gather the most helpful information to figure out why you’re not feeling well.

Keep the bandage for the length of time the clinician instructs you—this will reduce the risk of bruising. Should you experience phlebitis (also known as a swollen vein), you should alert your health provider. They may recommend elevating the affected arm and warm compresses.

Before the Test

If you have other tests done at the same time, you may be asked to fast for several hours before the blood sample is taken.

Good communication can help reduce any anxiety you feel surrounding your test. Your healthcare provider can explain the procedure in detail, provide any specific instructions you need to follow on the day of the test, and go over aftercare.

Make sure you have your insurance card with you and a form of identification so that there’s no delay in your ability to get the test. Most CO2 blood tests are often run as part of routine blood work. Consider speaking with your insurance carrier regarding the out-of-pocket expenses you could be responsible for paying so that you’re not surprised by an unexpected bill.

During the Test

Your blood will be drawn for a CO2 blood test in the typical way that many blood tests are done. Most likely, you’ll be seated in a chair and your healthcare provider will wrap an elastic band around your arm, which will temporarily restrict blood flow and allow them to locate a vein.

Once they have found a vein, they’ll prepare the area with a disinfectant using an alcohol pad or an alcohol-moistened cotton ball before inserting the needle to draw your blood.

After the needle has entered your vein, the clinician or technician will place a vial at the end of the syringe and collect a small amount of blood.

When they have drawn enough blood for the test, they’ll remove the elastic band and place a piece of gauze or a cotton ball over it. They may ask you to put pressure on the site for a minute or two before covering it with an adhesive. Generally, the test takes only a few minutes to complete.

Interpreting the Results

When you receive your test results, remember that they are a guide to help your healthcare provider figure out what’s going on with you and why you may not be feeling well. Also, tests performed at different labs may yield different results.

Keep in mind that a test that falls outside the normal values of the reference range doesn’t automatically indicate that you have a medical condition.

There can be other elements, such as medications you might be taking, that contribute to your results.

Normal Range

The normal range of a CO2 blood test in a basic metabolic panel is 23 to 29 millimoles per liter (mmol/L). The range can vary slightly depending on the lab analyzing your blood, so discuss your specific results with your healthcare provider.

High Carbon Dioxide

If you have too much CO2 in your blood, this could suggest:

• Dehydration
• Frequent use of medications like antacids
• Lung conditions like pulmonary edema and chronic obstructive pulmonary disease (COPD)
• Congestive heart failure with diuretic use
• Disorders affecting the adrenal glands like Cushing's disease
• Impaired kidney function (this can also cause too little CO2, as well)

Low Carbon Dioxide

If your blood levels indicate your CO2 is too low, this may point to:

• Hyperventilation, which causes respiratory alkalosis and a compensatory metabolic acidosis
• Excessive alcohol or drug consumption
• Malnutrition
• Hyperthyroidism (excessive thyroid activity)
• Complications from type 1 or type 2 diabetes such as ketoacidosis
• Impaired kidney function
• Adrenal gland insufficiency like Addison’s disease

Summary

A carbon dioxide (CO2) blood test measures the amount of CO2 in your body. Your CO2 level needs to stay within a certain range, but when it's too high (or too low) the blood test results can help your healthcare provider to identify and diagnose a health condition.

Various diseases and disorders can cause changes in CO2 levels, but keep in mind that not all findings outside of the normal ranges on a carbon dioxide blood test indicate a serious illness. Dehydration, for example, can cause high CO2 levels.

The blood test itself is straightforward and rarely leads to complications. Your healthcare provider will discuss the results with you.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. Bijapur MB, Kudligi NA, Asma S. Central Venous Blood Gas Analysis: An Alternative to Arterial Blood Gas Analysis for pH, PCO2, Bicarbonate, Sodium, Potassium and Chloride in the Intensive Care Unit Patients. Indian J Crit Care Med. 2019 Jun;23(6):258-262. doi:10.5005/jp-journals-10071-23176
2. MedlinePlus. Carbon Dioxide (CO2) in Blood.
3. MedlinePlus. CO2 blood test.
4. Icahn School of Medicine at Mount Sinai. CO2 blood test.

By Jenny Lelwica Buttaccio, OTR/L
Jenny Lelwica Buttaccio, OTR/L, is a licensed occupational therapist and advocate for patients with Lyme disease.

• Meet Our Medical Expert Board
• About Us
• Editorial Process
• Diversity Pledge
• Privacy Policy
• In the News
• Advertise
• Terms of Service
• Careers
• Contact
• EU Privacy

Verywell Health's content is for informational and educational purposes only. Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

We Care About Your Privacy

We and our 100 partners store and/or access information on a device, such as unique IDs in cookies to process personal data. You may accept or manage your choices by clicking below, including your right to object where legitimate interest is used, or at any time in the privacy policy page. These choices will be signaled to our partners and will not affect browsing data.

We and our partners process data to provide:

Store and/or access information on a device. Use limited data to select advertising. Create profiles for personalised advertising. Use profiles to select personalised advertising. Create profiles to personalise content. Use profiles to select personalised content. Measure advertising performance. Measure content performance. Understand audiences through statistics or combinations of data from different sources. Develop and improve services. Use limited data to select content. List of Partners (vendors)