White Blood Cell Count
At a Glance
Why Get Tested?
If your doctor thinks that you might have an infection or a disease that affects the production of white blood cells and to monitor treatment
When to Get Tested?
As part of a complete blood count (CBC), which may be ordered for a variety of reasons
Sample Required?
A blood sample drawn from a vein in your arm or by a fingerstick (children and adults) or heelstick (newborns)
Test Preparation Needed?
None
The Test Sample
What is being tested?
The white blood cell (WBC) count numerates the number of white blood cells in a sample of blood. An abnormal high or low count may suggest 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 there is an infection, white blood cells will attack and destroy the bacteria, fungus, or virus 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 a fingerstick (for children and adults) or heelstick (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 medications that weaken the immune system, such as HIV infection, chemotherapy, or radiation therapy cause a decrease in white blood cells. The WBC count detects dangerously low numbers of these cells.
The WBC count is used to determine the presence of an infection or leukemia. It is also used to help monitor the body’s response to various treatments and to monitor bone marrow function.
When is it ordered?
A WBC count is normally ordered as part of the complete blood count (CBC). In some circumstances, a WBC count may be ordered to monitor recovery from illness.
What does the test result mean?
An elevated number of white blood cells is called leukocytosis. This can result from bacterial infections, inflammation, leukemia, trauma, intense exercise, or stress.
A decreased WBC count is called leukopenia. It can result from many different situations, such as chemotherapy, radiation therapy, or diseases of the immune system.
Counts that continue to rise or fall to abnormal levels indicate that the condition is getting worse. Counts that return to normal indicate improvement.
Is there anything else I should know?
Pregnancy in the final month and labor may be associated with increased WBC levels.
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 are age-related.
On average, normal newborns and infants have higher WBC counts than adults.
It is not uncommon for the elderly to fail to develop leukocytosis as a response to infection.
There are many drugs that cause both increased and decreased WBC counts.
Smoking may also cause an increased WBC count.
Common Questions
Ask a Laboratory Scientist
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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.
S1
Thomas, Clayton L., Editor (1997). Tabers Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
S2
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosbys Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
S3
Susan J. Leclair, PhD, CLS(NCA). Professor of Medical Laboratory Science, Department of Medical Laboratory Science, University of Massachusetts, Dartmouth, MA.
S4
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosbys Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 1003-1008.
