White Blood Cell
Differential Count
At a Glance
Why Get Tested?
To diagnose an illness affecting your immune system, such as an infection or viral condition, or other diseases that affect your white blood cells, such as leukemias
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 (infants)
Test Preparation Needed?
None
The Test Sample
What is being tested?
There are five types of white blood cells, each with different functions: neutrophils, lymphocytes, monocytes, eosinophils and basophils. The differential reveals if these cells are present in normal proportion to one another, if one cell type is increased or decreased, or if immature cells are present. This information is helpful in diagnosing specific types of illnesses that affect the immune system.
White blood cells are made in your bone marrow. They protect your body against infection and aid your immune system. If an infection develops, white blood cells attack and destroy the microorganism causing the infection.
How is the sample collected for testing?
The test is performed on a blood sample drawn from a vein in the arm or from a fingerstick (for children and adults) or heelstick (for infants).
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?
The white blood cell differential assesses the ability of the body to respond to and eliminate infection. It also detects the severity of allergic and drug reactions plus the response to parasitic and other types of infection. It is essential in evaluating the reaction to viral infections and response to chemotherapy. It can also identify various stages of leukemia.
When is it ordered?
The white blood cell differential is normally run as part of the complete blood count (CBC), which is ordered for many different reasons.
What does the test result mean?
The results indicate the percentage of each type of white blood cell that is present.
Neutrophils can increase in response to bacterial infection or inflammatory disease. Severe elevations in neutrophils may be caused by various bone marrow disorders, such as chronic myelogenous leukemia. Decreased neutrophil levels may be the result of severe infection or other conditions, such as responses to various medications, particularly chemotherapy.
Eosinophils can increase in response to allergic disorders, inflammation of the skin, and parasitic infections. They can also increase in response to some infections or to various bone marrow disorders. Decreased levels of eosinophils can occur as a result of infection.
Basophils can increase in cases of leukemia, chronic inflammation, the presence of a hypersensitivity reaction to food, or radiation therapy.
Lymphocytes can increase in cases of viral infection, leukemia, cancer of the bone marrow, or radiation therapy. Decreased lymphocyte levels can indicate diseases that affect the immune system, such as lupus, and the later stages of HIV infection.
Monocyte levels can increase in response to infection of all kinds as well as to inflammatory disorders. Monocyte counts are also increased in certain malignant disorders, including leukemia. Decreased monocyte levels can indicate bone marrow injury or failure and some forms of leukemia.
Since percentages might be misleading in some patients, absolute values of the various types of WBCs can also be reported, such as the absolute neutrophil count (ANC), also known as the absolute granulocyte count or AGC. Absolute values are calculated by multiplying the number of WBCs by the percentage of each type of white cell and can aid in diagnosing illness and monitoring therapy.
Is there anything else I should know?
Eating, physical activity, and stress may alter white blood cell differential values.
Long-term use of steroids or long-term exposure to toxic chemicals (such as lye or insecticides) can increase the risk of an abnormal differential.
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.
