(1) Measurement of the total number of white blood cells in a sample of blood. Blood Count Information
(2) Leukocyte count; White blood cell count
A WBC count is a blood test to measure the number of white blood cells (WBCs).
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 blood flow. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
For an infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
A WBC count is almost always done as part of a CBC (complete blood count).
Risks A simple blood test is generally safe. In general, risks may include:
Excessive bleeding (rare) Fainting or feeling light-headed Hematoma (blood accumulating under the skin) Infection (a slight risk any time the skin is broken) Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.