Also Known As
Total CO2
TCO2
Carbon Dioxide Content
CO2 Content
Bicarb
HCO3
Formal Name
Bicarbonate
This article was last reviewed on
This article waslast modified on 29 October 2017.
At a Glance
Why Get Tested?

Usually as part of a renal profile (collection of tests which help investigate kidney function), 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 taken from a vein in the arm

Test Preparation Needed?

None

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you will be able to access your results online.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, gender, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

When you breathe, you bring oxygen (O2) into your lungs and release carbon dioxide (CO2). Carbon dioxide in your blood is present in three forms: carbonic acid (H2CO3), CO2 dissolved in blood, and bicarbonate (HCO3-), the predominant form. Bicarbonate is a negatively charged ion that is excreted and reabsorbed by your kidneys. Its function is to help maintain the acid-base balance (pH) and to work with sodium, potassium, and chloride to maintain electrical neutrality at the cellular level.

Measuring bicarbonate gives an estimation of acid-base balance. This is usually sufficient, but measurements of gasses dissolved in the blood may be done if more information is needed. Bicarbonate may be measured with sodium, potassium, and chloride in an electrolyte profile as it is the balance of these that gives your doctor the most information.

How is the sample collected for testing?

A blood sample is taken 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.

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Common Questions
  • How is it used?

    Bicarbonate levels are usually measured 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 water imbalance is upsetting your electrolyte balance;
    • to help evaluate your 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 or lower than normal, it suggests that your body is having trouble maintaining its acid-base 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. 

     Some of the causes of a low bicarbonate level include:

    Increased levels may be due to:

  • 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.

  • If bicarbonate levels are too high or low, what treatments can help?

    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 drugs), 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, for example, diabetic ketoacidosis, which can be treated in part by correcting the blood sugar (glucose) problem that led to the ketoacidosis.

  • What other gases circulate in blood?

    Oxygen, dissolved and bound to haemoglobin and vital for normal body function. Smokers and people who have been exposed to carbon monoxide may have measurable amounts of it in their blood. Carbon monoxide also binds to your red blood cells, diminishing your body's ability to carry oxygen.

  • If my doctor has measured bicarbonate, why do they want to do blood gases?

    Blood gas tests, in which blood is taken from an artery instead of a vein, can give your doctor a better assessment of your acid-base status and indicate whether you are taking in enough oxygen and getting rid of enough CO2.

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