| Subject | Contents |
| Definition | A test that measures the amount of carbon dioxide (CO2) in serum. Serum CO2 is really a measure of serum HCO3- (bicarbonate). This is because the procedure used to measure HCO3- in the laboratory first converts it to CO2. In the body, 95% of the CO2 is present as HCO3- so most of what is measured in the laboratory represents HCO3-. |
| Alternative Names | Bicarbonate test; HCO3- |
| How the test is performed | Adult or child: Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding . Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. CO2 and bicarbonate are also measured as part of an arterial blood gas analysis . |
| How to prepare for the test | The health care provider may advise you to discontinue drugs that may affect the test (see "Special considerations"). Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:infant test or procedure preparation (birth to 1 year) toddler test or procedure preparation (1 to 3 years) preschooler test or procedure preparation (3 to 6 years) schoolage test or procedure preparation (6 to 12 years) adolescent test or procedure preparation (12 to 18 years) |
| How the test will feel | When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed | The CO2 levels in the blood are influenced by kidney and respiratory (lung) function. |
| Normal Values | The normal range is 20-29 mEq/L. Note: mEq/L = milliequivalent per liter |
| What abnormal results mean | Lower-than-normal levels of HCO3- may indicate: ketoacidosis lactic acidosiskidney diseasediarrhea methanol poisoning salicylate toxicity (such as aspirin overdose) ethylene glycol poisoning Addison’s disease (adrenal gland insufficiency) Greater-than-normal levels of HCO3- may indicate: excessive vomitingrespiratory dysfunction (breathing disorders) hyperaldosteronismCushing’s syndrome Note: The kidneys are the organ primarily responsible for maintaining the normal levels of HCO3-. Metabolic acidosis (pH < 7.35 and hco3- < 20 meq/l) is a symptom of renal disease . However, HCO3- levels are also decreased in the presence of organic acids, (ketone bodies in diabetic acidosis '>ketoacidosis ) because HCO3- is used to neutralize the acids. Additional conditions under which the test may be performed: alkalosisdeliriumdementiarenal tubular acidosis; distalrenal tubular acidosis; proximal any medical condition in which the examiner feels there might be a metabolic derangement |
| What the risks are | excessive bleedingfainting or feeling light-headed hematoma (blood accumulating under the skin) infection (a slight risk any time the skin is broken) multiple punctures to locate veins |
| Special considerations | Drugs that can increase HCO3- measurements include corticosteroids and excessive use of antacids. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
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