White Blood Cell Count
At a Glance
Why Get Tested?
If your doctor thinks that you might have an infection, inflammatory illness, immune deficiency, bone marrow disease or allergy and; to monitor treatment
When to Get Tested?
As part of a full blood count (FBC), which may be requested for a variety of reasons
Sample Required?
A blood sample taken from a vein in your arm or from a finger-prick or in babies a heelprick
Test Preparation Needed?
None
The Test Sample
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 bone marrow and protect the body against infection and aid in the immune response. If an infection develops, white blood cells attack and destroy the micro-organism causing the infection.
How is the sample collected for testing?
The blood sample is obtained by a needle placed in a vein in the arm or from a finger-prick or heel-prick (for newborns).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
The Test
How is it used?
Conditions or drugs that weaken the immune system, such as HIV infection or chemotherapy, cause a decrease in white blood cells. The WBC count detects dangerously low numbers of these cells.
The WBC count is used to suggest the presence of an infection, an allergy, or bone marrow disorder. It is also used to help monitor the body's response to various treatments.
When is it requested?
A WBC count is part of the full blood count (FBC), which is requested for a variety of reasons. Changes in the WBC, whether it is high or low, may indicate a worsening or improvement in a medical condition.
What does the test result mean?
An elevated number of white blood cells is called leucocytosis. This can result from bacterial infections, inflammation, leukaemia, trauma, medication, or stress. A WBC count of 11.0–17.0x109/L cells would be considered mild to moderate leucocytosis.
A decreased WBC count is called leucopenia. It can result from many different situations, such as
- medication, especially chemotherapy, or radiotherapy
- vitamin deficiency, such as B12 or folic acid
- liver disease
- an enlarged spleen
- occasionally in inflammatory conditions such as rheumatoid arthritis or SLE
- some infections
- diseases of the immune system
A count of 3.0–4.0x109/L cells would be considered mild leucopenia.
Is there anything else I should know?
Increased WBC levels may be seen during the late stages of pregnancy.
If you have had your spleen removed, you may have a persistent mild to moderate increased WBC count.
The WBC count tends to be lower in the morning and higher in the late afternoon. WBC counts change with age with normal newborns and infants typically have a higher WBC counts than adults. It is not uncommon for the elderly to fail to develop leucocytosis (a high WBC) as a response to infection.
There are many drugs that cause both increased and decreased WBC counts.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
