Carbon Dioxide (CO2)

Optimal Result: 20 - 29 mEq/L, or 20.00 - 29.00 mmol/L.

Carbon dioxide (CO2) belongs to class of molecules called electrolytes, which are minerals in your blood and body fluid that carry an electric charge. Electrolytes have a variety of specialized functions including regulating the amount of water in the body, keeping the acidity of our blood balanced, and aiding muscles to function correctly—among others things. CO2 exists mostly commonly in our bodies in the form of a substance called bicarbonate (HCO3-). Therefore, the test to measure carbon dioxide in the body is really a measurement of bicarbonate levels. Typically, a bicarbonate test is ordered as a part of an electrolyte panel (along with sodium, potassium, and chloride), a basic metabolic panel (BMP), or a comprehensive metabolic panel (CMP). A healthcare professional will run these tests when the pH level of the blood is too acidic (acidosis) or alkaline (alkalosis) or when an acute condition presents with the following symptoms:

- Prolonged vomiting and/or diarrhea

- Weakness, fatigue

- Difficulty breathing

A pH imbalance in the blood can be caused primarily by a respiratory issue (the lungs are not effectively balancing the intake of oxygen and the release of carbon dioxide) or a metabolic issue (increased or decreased bicarbonate in the blood).

Additionally, the balance of bicarbonate and other electrolytes in the body is a good indicator of how well the heart and kidneys are functioning. 

What does it mean if your Carbon Dioxide (CO2) result is too low?

A low level may be caused by:

- Hyperventilation.
- Aspirin or alcohol overdose.
- Diarrhea, dehydration, or severe malnutrition.
- Liver or kidney disease.
- A massive heart attack.
- Hyperthyroidism or uncontrolled diabetes.
- A serious infection of the whole body (sepsis).


A low level of bicarbonate in the blood combined with a low pH (less than 7.4) is a condition called metabolic acidosis. Some common causes include: kidney failure, liver failure, severe diarrhea, lactic acidosis, seizures, cancer, prolonged lack of oxygen, and diabetic ketoacidosis. A low level of bicarbonate in the blood and a high pH (more than 7.4) is called respiratory alkalosis. Some common causes include: hyperventilation, fever, pain, and anxiety.

Drugs known to decrease bicarbonate levels include: methicillin, nitrofurantoin, tetracycline, thiazide diuretics, and triamterene. 

What does it mean if your Carbon Dioxide (CO2) result is too high?

A high level may be caused by:

- Vomiting.
- Dehydration.
- Blood transfusions.
- Overuse of medicines that contain bicarbonate (especially antacids).
- Conditions such as anorexia, chronic obstructive pulmonary disease (COPD), fluid in the lungs (pulmonary edema), heart disease, Cushing's disease, or Conn's syndrome.


A high level of bicarbonate and low pH (less than 7.4) is called respiratory acidosis and could indicate lung cancer, asthma, pulmonary hypertension, or exposure to toxic chemicals. A test result of high bicarbonate and high pH (more than 7.4) is called metabolic alkalosis. Common causes include: chronic vomiting, low potassium, or hypoventilation (slowed breathing).

Drugs known to increase bicarbonate levels include: barbiturates, steroids, hydrocortisone, fludrocortisone, and loop diuretics. 

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