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What Is a WBC?

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Updated April 29, 2009

Abnormal WBC results

Abnormal results might be a high WBC count or a low WBC count

Photo © A.D.A.M.
Definition: In a white blood cell count (WBC), a sample of blood is taken and examined under a microscope. To obtain the blood sample, a lab technician inserts a needle into a vein, usually in your arm in the inside of your elbow. Sometimes, especially in babies, the blood sample may be taken from a vein somewhere else on the body, like the back of the hand. The technician puts the blood sample in a vial and it is sent to the laboratory for analysis.

Blood is mainly composed of three types of cells: red cells, white cells, and platelets. In a WBC, the number and types of white blood cells present in the blood are measured. Normal results for a WBC range from 4,500-10,000 white blood cells/mcL (cells per microliter).

The information from the WBC can help diagnose and manage diseases. Many different diseases can cause changes in the numbers of white blood cells. For example, if an infection is present, the number of white blood cells may be higher, or if bone marrow failure is present, the number of white blood cells may be lower.

Also Known As: white cell count
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