| Marker | Gabriel optimal | Typical lab range | Functional range |
|---|---|---|---|
| CO2 (Bicarbonate) | 25 to 30 mmol/L | 20 to 29 | 26 to 31 |
What the CO2 test measures
Your lungs and kidneys work together to keep your blood's pH in a narrow range. Bicarbonate is the main base in the blood that soaks up acid. On a lab report the test may be called CO2, total CO2, bicarbonate or HCO3.
This is a blood test from a vein, not a breathing test. It is read together with sodium, chloride and potassium, and it is one of the numbers used to work out the anion gap.
What a low CO2 can mean
- Metabolic acidosis from kidney disease, liver disease or long-lasting diarrhea, which drains bicarbonate from the gut.
- Diabetic ketoacidosis, a serious complication of diabetes.
- Breathing too fast (hyperventilation), which blows off carbon dioxide.
- Shock and Addison disease (low adrenal hormones).
A result outside the range doesn't always mean a condition that needs treatment. Medicines and other factors can shift it, so your clinician reads it with your symptoms and other tests.
What a high CO2 can mean
- Vomiting or dehydration, which can lead to metabolic alkalosis.
- Diuretics (water pills) and low potassium, which often go together.
- Lung diseases that make it hard to breathe out carbon dioxide; the kidneys hold on to bicarbonate to balance it.
- Cushing syndrome or other states with too much of certain adrenal hormones.
- Long-term heavy use of calcium carbonate antacids.
A high CO2 is not a sign of better health. Gabriel's optimal band tops out at 30 mmol/L for that reason.
What to do with an abnormal result
- Look at the whole panel. Chloride, potassium, kidney tests and the anion gap help show which way the balance has tipped and why.
- Mention recent illness. Vomiting, diarrhea or a fast breathing spell can explain a result.
- List your medications, including diuretics and antacids.
- Ask whether a repeat test is needed. If the cause isn't clear, a clinician may order an arterial or venous blood gas, which measures pH directly.
Get urgent care if an abnormal CO2 comes with confusion, fast or deep breathing, trouble breathing, vomiting that won't stop, fruity-smelling breath with high blood sugar, or severe weakness.
Common questions
What is a normal CO2 level in a blood test?
Many labs use about 20 to 29 mmol/L for adults, and ranges vary by lab. Gabriel's optimal range is 25 to 30 mmol/L.
Is CO2 in a blood test the same as bicarbonate?
Mostly, yes. Most of the carbon dioxide in blood is carried as bicarbonate, so labs use total CO2 as a stand-in for bicarbonate.
What does a low CO2 level mean?
It can mean there is extra acid in the blood, for example from kidney disease, diarrhea or diabetic ketoacidosis, or that you were breathing fast. A clinician reads it with the rest of the panel.
Can diet change my CO2 level?
Large changes usually come from illness, medications or kidney and lung function, not from a single meal. Ask a clinician before trying to change it with food, baking soda or supplements.
Does a CO2 blood test check my lungs?
Indirectly. Lung disease can raise CO2, and fast breathing can lower it, but the test is mainly a check on acid-base balance. Lung function needs its own tests.
Sources
- Carbon Dioxide (CO2) in Blood MedlinePlus, U.S. National Library of Medicine
- Electrolyte Panel MedlinePlus, U.S. National Library of Medicine
- Metabolic Acidosis Merck Manual Professional Edition
- Metabolic Alkalosis Merck Manual Professional Edition
This guide is general information, not medical advice. It does not replace a visit with a licensed clinician. Gabriel membership is not health insurance.