Definition This test looks for the amount of carbon dioxide (CO2) in the blood. The real purpose of the test is to determine the blood level of bicarbonate (HCO3-). During laboratory testing, HCO3- is converted to CO2. That is why CO2 levels are measures to determine HCO3- levels. HCO3- is important in neutralizing acids. Its concentration in the blood is an indication of the ability of the kidneys and lungs to control acid-base balance.
Who is a candidate for the test? This test is ordered to help diagnose a wide variety of disorders in the body's basic functioning. This includes disorders of the kidney, adrenal gland, or breathing mechanisms. It is also helpful in diagnosing various poisonings.
How is the test performed? A sample of blood is taken in order to measure the CO2 level. The blood is usually drawn from a vein in the forearm or the hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A very thin needle is gently inserted into a vein and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial. The sample is sent to the laboratory to be analysed. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test? Individuals should receive instructions from their doctor.
What do the test results mean? Normal values for CO2 in blood range from 20 to 29 milliequivalents per litre (mEq/L).
Abnormally high levels may indicate:
vomiting
breathing disorders
hyperaldosteronism, or overproduction of hormones by adrenal gland
Cushing's syndrome, a disorder caused by too much corticosteroids, either from drugs, such as prednisone, or from natural production by the body
Addison's disease, a disorder causing low production of corticosteroids by the body
Author: Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
