The full blood count (FBC) is a common test that provides important information about the kinds and numbers of cells in the blood. It is used to check your general health and to help diagnose and monitor a variety of conditions and treatments.
What is an FBC test?
An FBC is a commonly ordered blood test in which a blood sample is taken from a vein in the arm and collected in a tube. This tube is sent to the laboratory for analysis.
Results of an FBC give information about the three main cells contained in your blood. These are:
- red blood cells
- white blood cells
The FBC test is important for diagnosing conditions in which the number of blood cells is abnormally high or abnormally low, or the cells themselves are abnormal.
When is an FBC test done?
An FBC test may be requested as a routine blood test to find out about your general health. It may also be used to help with diagnosis and monitoring of different conditions and treatments. For example, an FBC can be used:
- to investigate deficiencies such as vitamin B12 or folate deficiency or iron deficiency anaemia
- to help diagnose infection
- to help diagnose blood disorders
- to monitor the response to some types of medication or radiation treatment
- to investigate abnormal bleeding or clotting.
How to prepare for the test
You do not need to do anything before having this test.
How is the sample collected for testing
A blood sample is taken by a needle placed in a vein in the arm. An elastic band is wrapped around your upper arm. It may feel tight for a few seconds. You may feel nothing at all from the needle, or you may feel a small brief sting or pinch. The blood sample is collected in a tube, which is sent to the laboratory for analysis. Read more about blood tests.
Interpreting blood test results is not always easy and is best done in consultation with your healthcare team. They will know what is normal for you and how these results tie in with your clinical picture. Often, if there is a mild abnormality, all that may be needed is to repeat the test in a month or two's time as many changes can be temporary and return to normal.
On its own, an FBC cannot usually provide a definitive diagnosis of a condition, but it can provide important "clues" about possible problems with your health, such as:
- Low haemoglobin – indicates anaemia, which has a number of possible causes, including iron deficiency, internal bleeding or a poor diet.
- High haemoglobin – which may be caused by an underlying lung disease or problems with the bone marrow.
- A low white blood cell count – which may be genetic and of no significance, but could also be caused by problems with your bone marrow, or a viral infection.
- A high white blood cell count – which is usually suggestive of an infection somewhere in your body however rarely can be a sign of more serious illness.
- A low platelet count – which may be caused by a viral infection or an autoimmune condition (where the immune system attacks healthy tissue)
- A high platelet count – which may be caused by inflammatory conditions, infection or a problem with the bone marrow.
The following is further reading that gives you more information on the full blood count test. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.