Measurement of the levels of total CO2 (sometimes called bicarbonates) is ordered with sodium, potassium, and chloride testing when the physician suspects an electrolyte disorder combined with a problem in the pH balance of the blood (acid-base balance), including disorders caused by certain medications. Except perhaps for respiratory insufficiency and kidney insufficiency, significant disorders of the acid-base balance are rarely seen in outpatients who have no symptoms.
When total CO2 levels are too low, it may mean that the CO2 is being used to neutralize excess acids (diabetic ketoacidosis, kidney insufficiency, lactic acidosis, and methanol, ethylene glycol, or aspirin poisoning). Adrenal gland insufficiency (Addison’s disease), chronic diarrhea, and breathing too quickly (respiratory alkalosis) also cause lower CO2 levels.
High total CO2 levels in the blood can be caused by prolonged vomiting (metabolic alkalosis), respiratory diseases such as chronic obstructive pulmonary disease (COPD), and excessive secretion of cortisol (Cushing’s disease) or aldosterone (Conn’s syndrome) by the adrenal glands.