Carbon Dioxide, Total

Test ID:

702820

CPT code:

82374

Synonyms:

•CO2
•TCO2

Clinical Use:

Evaluate the total carbonate buffering system in the body, acid-base balance. High results may represent respiratory acidosis with CO2 retention, or metabolic alkalosis (eg, prolonged vomiting). Low value may indicate respiratory alkalosis as in hyperventilation or metabolic acidosis (eg, diabetes with ketoacidosis

Additional Test Information:

“Total carbon dioxide” consists of CO2 in solution or bound to proteins, HCO3−, CO32−, and H2CO3. In practice, 80% to 90% is present as bicarbonate (HCO3−). “Hypercapnia” means excessive carbon dioxide in the blood. Impaired elimination of CO2 reflects interaction of abnormalities in respiratory drive, the muscles of respiration, and the function of the lung. Elimination of carbon dioxide from the lung involves alveolar ventilation but not dead-space ventilation. Partitioning of these spaces is expressed as a ratio between dead space and total volume per breath: the tidal volume. The tidal volume normally is <0.30. These and other aspects of pulmonary gas exchange, ventilation and their consequences are addressed as the partial pressure of arterial carbon dioxide, PaCO2, a part of arterial blood gases.

Specimen Type:

Serum (preferred) or plasma

Requested Volume:

1 mL

Minimum Volume:

0.5 mL (Note: This volume does not allow for repeat testing.)

Container Type:

Gel-barrier tube (send entire tube) is preferred; red-top tube or green-top (heparin) tube is acceptable if centrifuged within 45 minutes and the serum or plasma is removed and placed in a tightly-stoppered secondary tube.

Collection:

Draw blood in gel-barrier tube and centrifuge. If red-top tube or green-top tube is used, centrifuge within 45 minutes of draw, remove the serum or plasma, and place in a transport tube and tightly stopper the tube.