Full Blood Count

What is a full blood count?

A full blood count is a blood test that is often done to assess the number and type of cells that circulate in the bloodstream. The three main types of cells that circulate in the blood are:

  • Red Cells (carry oxygen to the tissues)
  • White Cells (responsible for fighting infection)
  • Platelets (small sticky cells that prevent bruising and bleeding)

How is a full blood count performed?

A full blood count is performed by taking blood from a vein with a small needle. The blood is taken into a syringe and then placed in a tube with a small amount of anticoagulant to prevent the blood clotting. The liquid blood is then transferred to laboratory where it is placed in a specialised analyser that is designed to size and count the blood cells. The analyser provides a report on the number and type of cells in the blood and compares these results to "normal ranges" or normal values.

After a full blood count is performed a small amount of the blood is often placed on a glass slide to produce a "blood film" or "blood smear". The blood smear is then stained using a specialised series of dyes and then examined by a haematologist or haematology scientist under a microscope. The microscope magnifies the cells many thousands of times and can be used to examine the blood cells for any abnormalities.

What can a full blood count tell you?

A full blood count provides a lot of information about the number and types of cells in the blood. By comparing a patients full blood count results to the normal ranges, a number of conditions can be identified.

Examples of the conditions that can be identified with a full blood count are listed below:

  1. Anaemia – usually refers to a low haemoglobin which is derived from analysis of the red cell count. There are a number of causes for anaemia including iron deficiency. The type of anaemia can often be identified from a full blood count but other specialised investigations may be required.
  2. Leukaemia – leukaemia is generally referred to as a cancer of the white cells in the blood. Leukaemia may present with abnormalities in the blood counts including a low red-cell count (low haemoglobin), high white cell count and low platelets. Often a blood smear is required and is performed to further assess the type of leukaemia. Other specialised investigations including a bone marrow examination may be needed to fully assess the leukaemia subtype.
  3. Low platelets – platelets are small cells responsible for preventing bruising and bleeding. A full blood count is often one of the first tests performed if a patient presents with increased bruising or bleeding.

Many other conditions of the blood can be detected by performing a full blood count. Ask your doctor about the need for you to have a full blood count and to explain any abnormalities that have been detected with a full blood count.

FURTHER QUESTIONS?


The information presented in this fact sheet is intended as a general guide only. Patients should seek further advice and information about full blood counts and their individual condition from their treating haematologist or doctor.

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