HCO3-; Total CO2; TCO2
Usually as part of a renal profile (collection of tests which help investigate the kidney) to screen for an electrolyte or acid-base imbalance in conditions known to cause such disturbances, or to monitor a known imbalance
May be part of a routine blood test that includes electrolyte measurements or may be requested by your doctor if you have a medical condition or are experiencing symptoms that could indicate problems with the acid-base balance of your body
A blood sample drawn from a vein in the arm
When you breathe, you bring oxygen (O2) into your lungs and release carbon dioxide (CO2). The bicarbonate test measures the total carbon dioxide in your blood [present in three forms: carbonic acid (H2CO3, CO2 dissolved in blood, and HCO3- (bicarbonate, the dominant form)]. HCO3- is an electrolyte that is excreted and reabsorbed by your kidneys. Its main job is to help maintain the acid-base balance (pH) in your body and secondarily to work with sodium, potassium and chloride to maintain electrical neutrality at the cellular level. The bicarbonate test, since it measures all three forms at once, gives your doctor a rough estimation of acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood may be done if more information is needed. Bicarbonate may be measured along with sodium, potassium, and possibly chloride in an electrolyte profile as it is the balance of the three of four that gives your doctor the most information.
A blood sample is drawn by needle from a vein in the arm.
No test preparation is needed.
A bicarbonate level is almost always done along with other electrolytes to tell your doctor whether your sodium, potassium, chloride and bicarbonate levels are in balance. They may be measured as part of routine blood testing or when your doctor suspects an imbalance. Bicarbonate may also be measured when your doctor is evaluating your acid-base balance, to screen for an imbalance, and to monitor a known problem during treatment.
Bicarbonate testing may be requested, usually as part of an electrolyte profile when:
When bicarbonate levels are higher than normal, it suggests that your body is having trouble maintaining its pH balance either by failing to remove carbon dioxide or perhaps because of an electrolyte imbalance, particularly a deficiency of potassium. Both of these imbalances may be due to a wide range of dysfunctions. Bicarbonate elevations may be seen with chronic lung-related problems, such as emphysema, and metabolic problems, such as severe diarrhoea or prolonged vomiting (which can cause metabolic alkalosis - as a consequence of loss of both acid and potassium).
Low bicarbonate levels may be seen with respiratory alkalosis (which can be caused by hyperventilation), metabolic acidosis, shock, starvation, and during kidney failure.
Some drugs may increase bicarbonate levels especially diuretics such as frusemide (usually as a consequence of potassium deficiency). Other drugs may cause slightly low levels. Your doctor can advise if this appears to be a problem.
If your bicarbonate is high or low, your doctor will identify and treat the underlying cause. For example, high bicarbonate may be caused by emphysema, which may be treated with oxygen therapy and medications, or by severe diarrhoea or vomiting (which would be treated by treating the reason for the diarrhoea or vomiting). Low bicarbonate may be caused by diabetic ketoacidosis, which can be treated in part by treating the blood sugar problem that led to the ketoacidosis or kidney diseases.
Electrolytes, sodium, potassium, chloride
Conditions: Acidosis and alkalosis
RCPA Manual: bicarbonate