This test is used to determine the amount of bicarbonate, called HCO3, in the blood. The test actually measures the blood level of carbon dioxide, called CO2. During laboratory testing, HCO3 is converted to CO2. HCO3 is important in neutralizing acids. Its concentration in the blood gives an idea of how well the kidneys and lungs can control acid-base balance.
This test is ordered to help diagnose a wide variety of disorders in the body's basic functioning. This includes problems with the kidney, adrenal gland, or breathing systems. It is also helpful in diagnosing some types of poisonings.
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 rubber tube called a tourniquet is tied 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 into a syringe or vial. The sample is sent to the lab to be analyzed. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
Individuals should receive instructions from their doctor.
The normal value for CO2 in the blood is 23 to 29 mEq/L. Most of the carbon dioxide in the blood is in the form of bicarbonate. Either term can be used. The lungs and kidneys control the amount of bicarbonate in the blood. This keeps the blood from becoming too acidic. In order for a person to live, he or she must have neither too much acid nor too much base in the blood.
Carbon dioxide or bicarbonate can be too high or too low in the following conditions:
Author:David T. Moran, MD
Editor:Crist, Gayle P., MS, BA
Reviewer:Melinda Murray Ratini, DO