What Is CO2 in a Blood Test? Normal Bicarbonate Range Explained
Also known as: Bicarbonate, total CO2, HCO3 blood test
The CO2 measured on a routine blood panel is mostly bicarbonate — a buffer your body uses to keep blood pH stable. It reflects how well your lungs and kidneys are balancing acids and bases. A normal blood CO2 (bicarbonate) level is about 23–29 mmol/L; abnormal levels can point to breathing problems, kidney issues, or acid-base disorders.
CO2 normal range
| Category | Range (mmol/L) |
|---|---|
| Normal (adults) | 23–29 mmol/LSome labs use 22–30 |
| Low | < 23 mmol/LMetabolic acidosis or respiratory compensation |
| High | > 29 mmol/LMetabolic alkalosis or lung-related retention |
Reference ranges vary by laboratory. Use the range printed on your own report as the definitive comparison.
What high CO2 can mean
- Vomiting or dehydration (loss of acid)
- Chronic lung disease
- Certain diuretics
- Metabolic alkalosis
What low CO2 can mean
- Metabolic acidosis (e.g. kidney disease, diabetic ketoacidosis)
- Rapid breathing / hyperventilation
- Severe diarrhea
What to do about an abnormal result
- CO2 is interpreted with chloride and the anion gap to classify acid-base problems.
- Mild abnormalities are common and often reflect hydration or breathing patterns.
- Persistent or marked changes deserve a closer look at kidney and lung function.
Understand your own results
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Frequently asked questions
Is CO2 on a blood test the same as the CO2 I breathe out?
Not exactly. The CO2 on a metabolic panel mostly measures bicarbonate dissolved in your blood, which is closely related to but not the same as the carbon dioxide gas you exhale. Both reflect acid-base balance.
What does low CO2 mean?
Low CO2 (bicarbonate) often indicates metabolic acidosis, which can be caused by kidney disease, uncontrolled diabetes, or severe diarrhea. It can also occur when you breathe rapidly. It's evaluated alongside your other electrolytes.
Related biomarkers
Medically reviewed by Antonieta Rueda, MD and Ayham Shneker, MD · Last reviewed July 6, 2026
This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or your lab results.