This test is done as part of an electrolyte panel to screen for an electrolyte or acid-base imbalance or to monitor a known imbalance. Carbon dioxide is part of the gas exhaled (breathed out) during breathing.

The CO2 test measures the total amount of carbon dioxide in the blood, mostly in the form of bicarbonate (HCO3-). Bicarbonate is a negatively charged electrolyte that is excreted and reabsorbed by the kidneys. It is used by the body to help maintain the body's acid-base balance (pH) and secondarily to work with sodium, potassium, and chloride to maintain electrical neutrality at the cellular level. Since the CO2 test measures all three forms of carbon dioxide in the blood (bicarbonate, H2CO3 [also known as carbonic acid], and dissolved CO2) as a total CO2, it will give a rough estimate but not an exact determination of the bicarbonate concentration.


A blood sample is obtained by inserting a needle into a vein in the arm.


  • Adult/elderly: 23-30 mEq/L or 23-30 mmol/L (SI units)

  • Child: 20-28 mEq/L

  • Infant: 20-28 mEq/L

  • Newborn: 13-22 mEq/L

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.