Carbon Dioxide, Total

CPT: 82374
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Test Details

Synonyms

  • CO2
  • TCO2

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

15−27

31 d to 5 m

15−26

6 to 11 m

15−25

1 to 12 y

17−27

>12 y

18−29

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

Specimen Requirements

Specimen

Serum (preferred) or plasma

Volume

1 mL

Minimum Volume

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

Container

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.

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

Clinical Information

Special Instructions

Maintain specimen in a tightly-stoppered tube.

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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