Carbon Dioxide, Total

CPT: 82374
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Synonyms

  • CO2
  • TCO2

Special Instructions

Maintain specimen in a tightly-stoppered tube.


Expected Turnaround Time

Within 1 day


Related Documents


Specimen Requirements


Specimen

Serum (preferred) or plasma


Volume

1 mL


Minimum Volume

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


Container

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


Collection

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


Storage Instructions

Room temperature


Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3


Causes for Rejection

Improper collection and storage; improper labeling


Test Details


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).


Limitations

Interpretation requires clinical information and the other electrolytes.


Methodology

Enzymatic


Reference Interval

See table.

Age

Range (mmol/L)

0 to 30 d

16−29

31 d to 1 y

15−25

2 to 5 y

17−26

6 to 12 y

19−27

>12 y

20−29


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

Note: Total CO2 (Bicarbonate) results should be interpreted with caution, because escape of dissolved CO2 from the sample prior to analysis is inevitable and will vary among laboratory locations. This is because the measured total CO2 in serum decreases relative to the amount of time that the sample is open to the atmosphere. CO2 loss occurs the moment the stopper is removed from the vacutainer tube. Labcorp facilities follow rigorous quality processes in order to reduce the exposure of patient samples to the atmosphere and minimize CO2 loss, but even minor logistical variations at our laboratory locations may cause differences in the degree of CO2 loss.


Footnotes

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

LOINC® Map

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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