Carbon Dioxide (Bicarbonate)
A measure of bicarbonate, the body's main buffer against acidity.
| Typical reference range | 20–32 mmol/L |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Most carbon dioxide in blood exists as bicarbonate, which neutralizes acids. The kidneys and lungs regulate its level to keep blood pH in a narrow range.
Why it matters
Abnormal CO2 points to acid-base disturbances caused by kidney, lung or metabolic problems.
What a high result can mean
High values suggest metabolic alkalosis, as from vomiting, diuretics, excessive antacid or bicarbonate use, or compensation for chronic lung disease with CO2 retention.
What a low result can mean
Low values suggest metabolic acidosis (kidney disease, diabetic ketoacidosis, lactic acidosis, severe diarrhea) or compensation for hyperventilation. Mildly low values are common if the tube is underfilled or left open.
What affects the result
Underfilled tubes and delayed processing falsely lower CO2. Intense exercise before testing can lower it. Interpret with chloride and anion gap.
Units and conversion
Usually reported in mmol/L.
- From mEq/L: multiply by 1 to get mmol/L
Also called on lab reports
Carbon Dioxide, CO2, Bicarbonate, Carbon Dioxide, Total, Total CO2, HCO3, CO2, Total, Bicarbonate (CO2), TCO2
Related tests: Electrolytes & Minerals
This page is educational and does not replace advice from a healthcare professional.