Bicarbonate (total CO2)
Main form of carbon dioxide in the blood and a marker of acid-base balance
Also known as
Definition
Most of the carbon dioxide (CO2) in the blood is present as bicarbonate (HCO3-), an electrolyte that helps regulate acid-base balance. The lab value total CO2 in serum therefore essentially reflects the bicarbonate level. It is part of the electrolyte panel and the basic metabolic panel and is influenced by how well the kidneys and lungs work.
| Parameter | Value |
|---|---|
| Unit | mmol/l (= mEq/l) |
| Reference Range | Typically about 23–29 mmol/l in adults. Labs differ slightly; the reference range on your own report is what counts. Discuss any deviation with your doctor. |
Agree on your personal target range with your doctor.
For bicarbonate, 1 mmol/l equals exactly 1 mEq/l because the ion carries a single charge. The numbers are the same in both units.
↓ What a low value means
A low value can be linked to metabolic acidosis, meaning the blood is too acidic, for example with kidney disease, long-lasting diarrhea, ketoacidosis or lactic acidosis. Other possible links include Addison disease, compensated respiratory alkalosis such as from hyperventilation, certain medicines such as carbonic anhydrase inhibitors, and poisoning, for example with salicylates. It is interpreted together with other values; discuss it with your doctor.
↑ What a high value means
A high value can be linked to metabolic alkalosis, for example after vomiting or fluid loss, or to lung diseases in which the body compensates for respiratory acidosis. Other possible links include Cushing syndrome, hyperaldosteronism, heart failure, heavy sweating and rare conditions such as Bartter syndrome. Medicines can also change the value. Discuss the result with your doctor.
When to test
Bicarbonate is usually measured as part of an electrolyte or basic metabolic panel: during routine checkups, with symptoms such as breathing problems, confusion, weakness, fatigue or long-lasting vomiting or diarrhea, and to check medicines that affect electrolyte balance. List all your medicines, but do not stop anything without medical advice. Other tests on the same sample may require fasting.
Frequently asked questions
Is total CO2 the same as bicarbonate? +
Almost. Most of the carbon dioxide in the blood is present as bicarbonate, so the serum CO2 value is used as a measure of the bicarbonate level. An arterial blood gas test is a separate test.
Why do the kidneys and lungs affect the value? +
The lungs breathe out carbon dioxide, and the kidneys keep the bicarbonate level in its usual range. If either organ is not working as usual, acid-base balance can shift and the value can change.
Can medicines change the bicarbonate value? +
Yes. Various prescription and over-the-counter medicines can raise or lower the value. Tell your doctor what you take, and do not stop anything on your own.
Does a value outside the reference range mean I have a disease? +
Not necessarily. An unusual value does not always need treatment; further tests often follow to put it in context. What your result means is something to clarify with your doctor.
Bicarbonate (total CO2)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.