What to know about the CO2 blood test


The CO2 blood test measures the amount of carbon dioxide in the blood, which is present in the form of CO2, bicarbonate (HCO3), and carbonic acid (H2CO3). It mainly occurs in the form of bicarbonate.

As part of its normal functions, the human body naturally produces certain acids and bases that balance each other. Any disruption to this balance can be an early sign of an underlying medical condition.

Carbon dioxide is an "acidic" component because it combines with water to form carbonic acid. This makes the blood acidic. The CO2 blood test detects changes in the blood's acidic content.

A healthcare professional can measure the levels of CO2 in a person's blood using a simple blood test. They may take blood from either an artery (an arterial blood draw) or a vein (a venous blood draw).

A venous blood draw provides a measure of bicarbonate levels. An arterial blood draw measures the particle pressure of carbon dioxide. Both components are indicators of blood oxygenation.

The test procedure usually takes around 2–5 minutes. A nurse or healthcare professional will make a tiny prick in the person's arm and collect blood in a test tube to send away for testing.

It is normal to experience a slight feeling of discomfort from where the nurse drew the blood, but this is temporary and will resolve on its own.

When do people need a CO2 test?

A healthcare professional may order a CO2 as part of a routine check-up or to investigate the underlying cause of certain symptoms. They may also recommend it in the case of a medical emergency or just before surgery.

People experiencing the following symptoms may receive a CO2 blood test:

  • nausea or vomiting
  • shortness of breath
  • breathing difficulties
  • confusion or feelings of faintness

A healthcare professional will likely perform a CO2 blood test as part of an electrolyte panel to check a person's bicarbonate, a form of CO2, levels.

This test measures levels of electrolytes, including sodium, chloride, and potassium in the blood, along with bicarbonate levels. Electrolytes keep the body's fluid balance in check and help maintain heart rhythm, muscle contractions, and brain function.

The electrolyte panel tells doctors how well a person's kidneys are functioning. High or low bicarbonate levels can indicate that a person has metabolic alkalosis or acidosis, respectively.

Both arterial and venous blood draws can provide an overall picture of a person's electrolyte status and the balance of acids and bases in their blood.

Media Contact:
John Mathews
Journal Manager
Journal of Phlebology and Lymphology
Email: phlebology@eclinicalsci.com