Maintain specimen in a tightly-stoppered tube.
Within 1 day
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Serum (preferred) or plasma
1 mL
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.
Room temperature
Temperature
Period
14 days
Refrigerated
Frozen
Freeze/thaw cycles
Stable x3
Improper collection and storage; improper labeling
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.
Enzymatic
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
“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
