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Alternate Names

  • bicarbonate
  • carbon dioxide
  • total carbon dioxide
  • HCO3-
  • "bicarb"
  • T CO2
  • CO2 content


This test is used to determine the amount of bicarbonate, called HCO3 (H for hydrogen, C for carbon, 03 for 3 oxygen molecules), in the blood.

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 may include problems with the kidney, adrenal gland, stomach and bowels (either vomiting or diarrhea) ,or lungs.
It is also helpful in diagnosing some types of poisonings. For example, people who drink radiator fluid (ethylene glycol) inadvertently or in a suicide attempt develop a severe acidosis, and therefore, drop there C02 or bicarbonate level.

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 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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
On some occasions the blood may be drawn from an artery (usually the radial or one of the "wrist" arteries).

What is involved in preparation for the test?

Individuals should receive instructions from their doctor. Most of the time no preparation is required.

What do the test results mean?

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 are designed to control the amount of bicarbonate in the blood. This keeps the blood from becoming too acidic or basic.

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:

  • Kidney problems (usually acid)
  • Breathing or lung problems (can be either acid or basic)
  • Poisonings or drug overdoses (usually acid)
  • Severe diarrhea (usually acid)
  • Uncontrolled diabetes (usually acid)
  • Severe dehydration leading to kidney under-function (usually acid)
  • vomiting (usually base)
  • over use of water pills (diuretics) (usually base).

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