The health care provider will take blood from your vein. The blood collects into an airtight container.
In infants or a young child, blood will be taken from a heel stick or finger stick. The blood is collected in a small glass tube or onto a slide or test strip.
Cotton or a bandage may be applied to stop any bleeding.
A laboratory specialist takes a drop of blood from your sample and smears it onto a glass slide. The smear is stained with a special dye, which helps tell the difference between various types of white blood cells.
Five types of white blood cells, also called leukocytes, normally appear in the blood:
Lymphocytes (B cells and T cells)
A computer or the health care provider counts the number of each type of cell. The test shows if the number of cells are in proper proportion with one another, and if there is more or less of one cell type.
How to prepare for the test
No special preparation is necessary.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is done to diagnose an infection, anemia, and leukemia. It may also be used to see if treatment for any of these conditions is working.
Neutrophils: 40% to 60%
Lymphocytes: 20% to 40%
Monocytes: 2% to 8%
Eosinophils: 1% to 4%
Basophils: 0.5% to 1%
Band (young neutrophil): 0% to 3%
What abnormal results mean
Any infection or acute stress increases your number of white blood cells. High white blood cell counts may be due to inflammation, an immune response, or blood diseases such as leukemia.
It is important to realize that an abnormal increase in one type of white blood cell can cause a decrease in the percentage of other types of white blood cells.
An increased percentage of neutrophils may be due to:
A decreased percentage of basophils may be due to:
Acute allergic reaction
What the risks are
There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Dinauer MC, Coates TD. Disorders of phagocyte function and number. In: Hoffman R, Benz EJ Jr, Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2008:chap 50.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.