CO2 / Bicarbonate

Measured in mmol/L

A measure of bicarbonate, the buffer your body uses to keep blood acidity steady — informative mainly alongside the other electrolytes, not alone.

What it is

This test measures the total carbon dioxide in your blood, which is mostly bicarbonate — a chemical buffer your kidneys and lungs use together to keep your blood from becoming too acidic or too alkaline. It's read as part of the electrolyte panel and often used with sodium and chloride to calculate the anion gap, a rough check on acid-base balance. Despite the name, it isn't a lung-function test, and values can drift with breathing patterns, vomiting, kidney function, or some medications, so it's interpreted in context rather than as a standalone number.

Typical range

  • Adults22–29 mmol/L

Source · Mayo Clinic Laboratories (HCO3) (2026)

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

  • What does my CO2/bicarbonate result suggest when you look at it with my other electrolytes?
  • Could anything I'm taking or any recent illness be shifting this value?
  • Is this a number you'd want to recheck over time, or is it stable enough not to follow?