Bicarbonate
Bicarbonate or total CO2 is different from the partial pressure of CO2 (PCO2).
To learn about PCO2 see blood gases.
At a Glance
Why Get Tested?
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
When to Get Tested?
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
Sample Required?
A blood sample drawn from a vein in the arm
Test Preparation Needed?
None
The Test Sample
What is being tested?
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.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
The Test
How is it used?
Bicarbonate levels are 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.
When is it requested?
Bicarbonate testing may be requested, usually as part of an electrolyte profile when:
- you are having a routine blood test
- your doctor suspects that you may be retaining water or are dehydrated, upsetting your electrolyte balance
- to help evaluate your body's acid-base balance (pH)
- to monitor a condition or treatment that might cause an electrolyte imbalance.
What does the test result mean?
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.
Is there anything else I should know?
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.
Common Questions
Ask a Laboratory Scientist
* indicates a required field!
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
