Page last updated April 2020

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CO2 Content

CO2 Content is a measurement of all the CO2 in the blood. 

Most of this is in the form of bicarbonate (HCO3), controlled by the kidney. A small amount (5%) of the CO2 is dissolved in the blood, and in the form of soluble carbonic acid (H2CO3).

For this reason, changes in CO2 content generally reflect such metabolic issues as renal function and unusual losses (diarrhea). Respiratory disease can ultimately effect CO2 content, but only slightly and only if prolonged.

Elevated CO2 levels are seen in:

  • Severe vomiting
  • Use of mercurial diuretics
  • COPD
  • Aldosteronism

Decreased CO2 levels are seen in:

  • Renal failure or dysfunction
  • Severe diarrhea
  • Starvation
  • Diabetic Acidosis
  • Chlorthiazide diuretic use


Normal Values*

Men 23-30 mmol/L


21-30 mmol/L
Pregnancy 18-25 mmol/L

*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.