Carbon Dioxide, Total

CPT: 82374
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  • CO2
  • TCO2

Special Instructions

Maintain specimen in a tightly-stoppered tube.

Expected Turnaround Time

Within 1 day

Related Documents

Specimen Requirements


Serum (preferred) or plasma


1 mL

Minimum Volume

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


Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.


Separate serum or plasma from cells within 45 minutes of collection.

Storage Instructions

Room temperature

Stability Requirements



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Improper collection and storage; improper labeling

Test Details


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).


Interpretation requires clinical information and the other electrolytes.



Reference Interval

See table.


Range (mmol/L)

0 to 30 d


31 d to 1 y


2 to 5 y


6 to 12 y


>12 y


Additional 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.1


1. Weinberger SE, Schwartzstein RM, Weiss JW. Hypercapnia. N Engl J Med. 1989 Nov 2; 321(18):1223-1231. 2677729


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
001578 Carbon Dioxide, Total 2028-9 001578 Carbon Dioxide, Total mmol/L 2028-9

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