Carbon Dioxide (CO2)

CPT Code: 82374
Specimen: Serum or Heparinized 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.
Methodology: Enzymatic
Collection: Sample should be analyzed as promptly as possible after collection and centrifugation of the blood in the unopened tube.

Total carbon dioxide concentration may be lowered by as much as 6 mmol/L when uncapped specimens are exposed to the air for one hour.

Underfilling of vacutainers may account for low total carbon dioxide results of up to 3 mmol/L.


Reference Range:

21-32 mmol/L


Temperatures Period 
Room Temperature 8 Hours
Refrigerated (2-8 ⁰C) 2 Days
Frozen (≤ -20 ⁰C) 6 Months


Use: Used to evaluate the total carbonate buffering system in the body, acid-base balance.  Carbon dioxide—often measured in its total form—serves as an indicator of water and acid-base balance in body fluids. Interpretation requires clinical information and evaluation of the other electrolytes (sodium, potassium, and chloride).
Clinical Significance:

High carbon dioxide results may represent respiratory acidosis with CO2 retention, or metabolic alkalosis (eg, prolonged vomiting).

Low carbon dioxide may indicate respiratory alkalosis as in hyperventilation or metabolic acidosis (eg, diabetes with ketoacidosis).

Causes for Rejection:  

Improper collection and storage; improper labeling

Interfering Substances:  

Hemoglobin (hemolysate) of 1000 mg/dL (monomer) decreases an ECO2 result of 13 mmol/L by 21%. Lipemia of 3000 mg/dL decreases an ECO2 result of 13 mmol/L by 16%. In rooms with poor ventilation, an open Flex reagent cartridge can absorb CO2 which may cause results to be elevated by up to 3