Carbon Dioxide Lab Test

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

The carbon dioxide lab test, also known as total CO2 or bicarbonate, is a measure of bicarbonate in the blood. This is because the majority of CO2 (about 75%) produced during cellular respiration, is carried in the blood in the form of bicarbonate ions. 20% of carbon dioxide remains combined with hemoglobin and other plasma proteins, while the remaining 5% is found in solution as dissolved Co2. The dissolved CO2 that is formed in the lungs contributes little to the CO2 value.[1],[2]


  • CO2, as bicarbonate, contributes to acid-base balancing. A carbon dioxide lab test is typically part of an electrolyte panel to identify or monitor an electrolyte imbalance or acid-base (pH) imbalance.
  • Metabolic acids, such as hydrochloric acid and lactic acid, are neutralized by bicarbonate.
  • Bicarbonate acts as one of the reserve alkaline elements in the blood.

Patient Preparation

  • No fasting is required.
  • Factors which can cause increased levels
Drugs: aldosterone, barbiturates, bicarbonates, ethacrynic acid, hydrocortisone, loop diuretics, mercurial diuretics, and steroids
  • Factors which can cause decreased levels
  • underfilling the tube with blood allows CO2 to escape from the serum specimen
  • Drugs: methicillin, nitrofurantoin (Furadantin), paraldehyde, phenformin, tetracycline, thiazide diuretics, and triamterene.

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 23-32 mEq/L 23-32 mmol/L
Optimal Range 25-30 mEq/L 25-30 mmol/L
Alarm Ranges < 18 or > 38 mEq/L < 18 or > 38 mmol/L

High levels indicate:

Low levels indicate:

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain.