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Alternative namesLeukocyte count; White blood cell count
DefinitionThis is a blood test to measure the number of white blood cells (WBCs). It is almost always part of the CBC (complete blood count). See also blood differential .
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to prepare for the test
No special preparation is necessary for adults.
For infants and children:
How the test will feelWhen 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 performedTo measure the number of white blood cells in the blood. White blood cells are the major infection-fighting cells in the body. They are also involved in reactions to allergies, tumors, and stress in general.
Normal Values4,500-10,000 white blood cells/mcl (cells per microliter)
What abnormal results meanLow numbers of WBCs (leukopenia) may indicate:
This test may be performed under many conditions and in many disease states.
What the risks areRisks associated with having blood drawn are slight:
There are several types of white blood cells (WBCs) that normally appear in the blood: neutrophils (polymorphonuclear leukocytes; PMNs), band cells (slightly immature neutrophils), T-type lymphocytes (T cells), B-type lymphocytes (B cells), monocytes, eosinophils , and basophils.
Any infection or sudden stress will result in an increased production of WBCs. This usually means increased numbers of cells and an increase in the percentage of immature cells (mainly band cells) in the blood. This change is called a "shift to the left."
Update Date: 6/1/2003Marcia S. Brose, M.D., Ph.D., Division of Hematology/Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT