At a glance

Also known as

HCO3-; Total CO2; TCO2

Why get tested?

Usually as part of a renal profile (a panel 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 acid-base imbalance

When to get tested?

Bicarbonate is usually part of a routine blood test that includes electrolyte measurements. It 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
 

What is being tested?

When we breathe, we take oxygen from the air into the body, and remove carbon dioxide (CO2), a waste gas produced by cells.  Most of the CO2 in the blood is converted to bicarbonate.  The bicarbonate blood test is also known as “total CO2” as it measures the CO2 dissolved in the blood as bicarbonate..

Bicarbonate is an electrolyte which is dissolved in the blood. It is important in maintaining the pH of the blood within the normal range.

The bicarbonate test gives your doctor a rough estimation of your body's acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood may be required if more information is needed. Bicarbonateis usually measured along with other electrolytes such as sodium, potassium, and possibly chloride. This gives your doctor more information about the acid-base and electrolyte status of the blood.

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 is almost always requested as part of an electrolyte panel/profile.  In the first instance, the bicarbonate result informs your doctor about the likely acid-base status of the blood.  When taken into consideration with the other electrolyte results, it is often possible to diagnose more specific types of acid-base balance disturbance.
 

When is it requested?

Some of the most common reasons to measure bicarbonate include the following:

  • As part of a routine health check.
  • If you are at risk of an acid-base disturbance (e.g. if you are taking medications known to affect bicarbonate levels in the body).
  • If you have symptoms of an acid-base or electrolyte imbalance (there are many such symptoms, your doctor will be best placed to advise on this).

What does the test result mean?

Bicarbonate results above the reference interval usually mean that your body is either losing too much acid, the lungs are failing to get rid of unwanted CO2, or that the kidneys are not getting rid of excess bicarbonate.  Common causes of a high bicarbonate include:

  • A chronic lung disease such as COPD
  • Prolonged vomiting
  • Use of certain drugs such as diuretics

Bicarbonate results that are below the reference interval usually indicate the build-up of acid in the blood (acidosis).  Common causes of a low bicarbonate include:

  • Chronic kidney disease
  • Poorly-controlled diabetes
  • Chronic, severe diarrhoea
  • Severe infection (sepsis)

Reference Intervals

Adult
22-32 mmol/L
Paediatric
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

The reference intervals shown above are known as a harmonised reference intervals. This means that eventually all laboratories in Australia should use the same interval so that wherever your sample is tested, the reference interval should be the one shown above. Laboratories are in the process of adopting these harmonised intervals so it is possible that the intervals shown on the report of your results for this test may be slightly different until this change is fully adopted. More information can be found under Reference Intervals – An Overview.
 

Is there anything else I should know?

Some drugs may increase bicarbonate levels such as diuretics e.g. frusemide or Lasix. Often other electrolytes will also be low e.g. sodium, potassium. Similarly some drugs may cause slightly low bicarbonate levels. Your doctor can advise if this appears to be a problem.

Occasionally a low bicarbonate may occur due to a laboratory error.  This is most common if there has been a prolonged delay between collecting the sample and analysis in the laboratory, or if the specimen tube was uncapped before being analysed.  Your doctor can discuss any such cases with the laboratory directly.
 

Common Questions

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 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.

What other gases circulate in blood?

Oxygen, both dissolved and bound to haemoglobin, is vital to the functioning of all cells in the body. Smokers and people who have been exposed to carbon monoxide may have measurable amounts of it in their blood. Carbon monoxide also binds to haemoglobin, diminishing your body's ability to carry oxygen. Nitrogen, from air, is dissolved in blood at low concentrations but is usually not of any significance.

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

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 (acid/base status) and indicate whether your body is taking in enough oxygen and getting rid of enough CO2.

Last Review Date: May 30, 2022


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