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This test measures the total carbon dioxide in your blood. It checks for an electrolyte or acid-base (pH) imbalance and is almost always done along with other electrolytes to show whether your sodium, potassium, chloride, and bicarbonate levels are in balance. It is often ordered as part of a renal profile, a collection of tests that help investigate the kidneys.

Why get 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 which is present in three forms: 

  • carbonic acid, 
  • carbon dioxide dissolved in blood, and
  • bicarbonate, the dominant form.

Your body needs bicarbonate to help keep a normal acid-base (pH) balance. Bicarbonate also works together with sodium, potassium and chloride to maintain electrical neutrality in the cells.

Since it measures all three forms of carbon dioxide at once, the bicarbonate test gives your doctor a rough estimation of acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood may also be done if more information is needed.  Blood gas tests, in which blood is drawn from an artery instead of a vein, can give your doctor a more accurate assessment of the body's pH status and show whether your body is taking in enough oxygen and getting rid of enough carbon dioxide.

Bicarbonate may also be measured along with sodium, potassium, and possibly chloride in an electrolyte profile as it is the balance of three out of four that gives your doctor the most information.


Having the test



Any preparation?


Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.


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 because of an electrolyte imbalance, particularly a deficiency of potassium. Both of these imbalances may be due to a wide range of problems. 


High levels can be caused by severe vomiting, dehydration, chronic lung-related problems, such as emphysema, and some hormonal disorders such as Cushing's disease.


Low levels are associated with kidney disease, chronic diarrhoea, diabetic ketoacidosis, Addison's disease.

Some medications can increase bicarbonate levels especially diuretics. Other drugs may cause slightly low levels. Your doctor can advise if this appears to be a problem.


Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

  • Reference intervals are the range of results expected in healthy people. 
  • When compared against them your results may be flagged high or low if they sit outside this range.
  • Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.


Bicarbonate Reference Intervals

The reference intervals for this test are common reference intervals which means that most laboratories in Australia should be using this same target range.

Adult: 22-32 mmol/L


0 to <1 week          15-28mmol/L

1 week - 2 years     16-29 mmol/L

2 years - 10 years   17-30 mmol/L

10 years - 18 years 20-32 mmol/L

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

  • Why does this test need to be done?
  • Do I need to prepare (such as fast or avoid medications) for the sample collection?
  • Will an abnormal result mean I need further tests?
  • How could it change the course of my care?
  • What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record.

You and your healthcare provider can now access your results whenever and wherever needed.Get further trustworthy health information and advice from healthdirect.

Last Updated: Thursday, 1st June 2023

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