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Bicarbonate (CO2) test

Also called: CO2, Total CO2, HCO3

The bicarbonate (CO2) test shows the acid-base balance in your blood. It's part of the basic metabolic panel.

SampleA small tube of blood from a vein in your arm
Fasting?Usually not needed
ResultsOften the same day
Good to knowOne result rarely tells the whole story. Your provider looks at your results together with your symptoms, exam, and other tests.

What the test is

Low bicarbonate can mean too much acid in the blood.

Why it's done

  • Part of routine metabolic panels
  • Vomiting, diarrhea, breathing problems, or diabetes concerns

Getting ready and what happens

  • No special preparation is needed.

How the test is done

  • A health worker cleans the skin, puts a band around your arm, and draws blood from a vein with a small needle. It takes a few minutes.

What the results mean

ResultTypical range for adults
CO2About 23 to 29 mEq/L

Normal ranges vary from lab to lab and can differ by age, sex, and pregnancy. Your report lists your lab's own range next to each result. A result a little outside the range is often not a problem.

Low

Can point to diarrhea, kidney disease, diabetic ketoacidosis, or certain poisonings.

High

Often from vomiting, water pills, or long-term lung disease.

Questions to ask your provider

  • What do my results mean for me?
  • Do I need to repeat this test or have other tests?

Risks

A blood draw is very safe. You may have slight pain or a small bruise where the needle went in.

Related conditions

Related tests

Sources

Last updated 2026-11-13.