At a glance
Also known as
WBC; WCC; leukocyte count; white count; white cell count
Why get tested?
To screen for or diagnose a variety of conditions that may affect the number of white blood cells (WBCs) such as an infection, immune deficiency, bone marrow disease, inflammation, allergy or a disease that affects the WBCs and to monitor treatment
When to get tested?
As part of a full blood count (FBC), when you have a routine health examination, when you have signs and/or symptoms that could be related to a condition that affects the WBC count or are undergoing treatment that affects WBCs.
A blood sample drawn from a vein in your arm or by a fingerprick or in the case of newborns a heelprick.
Test preparation needed?
What is being tested?
The white blood cell (WBC) count indicates the number of white blood cells in a sample of blood. This count provides a clue to the presence of illness. White blood cells are made in the and protect the body against infection and aid in the immune response. If an infection develops, white blood cells attack and destroy the or other micro-organisms causing the infection.
Blood is composed of three main types of cells; red blood cells, white blood cells and platelets that are suspended in fluid, called plasma. All these cells are made in the bone marrow and are released into circulation throughout the body.
There are five types of WBCs that each have a different function:
- Three types are referred to as Granulocytes because they contain granules in their cytoplasm that release chemicals as part of the immune response, these include:
- neutrophils: most common type of circulating WBCs. These cells move to the damaged or infected tissue where they engulf and destroy bacteria
- eosinophils: respond to infections caused by parasites, play a role in allergic reactions and control the extent of immune responses
- basophils: least commonly found in circulation and are involved in allergic reactions.
- Lymphocytes: these cells exist in the lymphatic system and blood and are sub divided into three types:
- B lymphocytes (B cells): produce antibodies as part of the immune response
- T lymphocytes (T cells): recognise foreign substances and processes them for removal
- Natural Killer cells (NK cells): directly attack and destroy cancerous cells or cells infected with a virus
- Monocytes: similar to neutrophils, migrate to the site of infection, engulf and destroy bacteria.
When a person has an inflammatory process or infection somewhere in the body, the bone marrow will produce more WBCs and release them into the circulation where they migrate to the site of inflammation or infection. The bone marrow will cease to produce WBCs and levels will drop back to normal when the condition resolves.
Immune disorders and cancer can also affect the production of WBCs by the bone marrow, this will result in either an increase or decrease number of WBCs in the blood. Results are often interpreted along with a WBC differential.
Find out about the Full Blood Count
How is the sample collected for testing?
The blood sample is obtained by a needle placed in a vein in the arm or by a fingerprick or heelprick (for newborns).
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.