Health Encyclopedia

WBC count

Definition

A WBC count is a blood test to measure the number of white blood cells (WBCs).

White blood cells help fight infections. They are also called leukocytes. There are five major types of white blood cells:

Basophils
Eosinophils
Lymphocytes (T cells and B cells)
Monocytes
Neutrophils

Alternative Names

Leukocyte count; White blood cell count

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 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).

How to prepare for the test

No special preparation is usually needed.

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

The test is performed to find out how many white blood cells you have. Your body produces more white blood cells when you have an infection or allergic reaction -- even when you are under general stress.

Normal Values

4,500-10,000 white blood cells/mcL (cells per microliter)

What abnormal results mean

A low number of WBCs is called leukopenia. It may be due to:

Bone marrow failure (for example, due to infection, tumor, or abnormal scarring)
Collagen-vascular diseases (such as lupus erythematosus)
Disease of the liver or spleen
Radiation

A high number of WBCs is called leukocytosis. It may be due to:

Anemia
Infectious diseases
Inflammatory disease (such as rheumatoid arthritis or allergy)
Leukemia
Severe emotional or physical stress
Tissue damage (for example, burns)

These lists are not all inclusive.

What the risks are

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.

Special considerations

People who have had their spleen removed (splenectomy) will always have a slightly higher number of WBCs.

Drugs that may increase WBC counts include:

Allopurinol
Aspirin
Chloroform
Corticosteroids
Epinephrine
Heparin
Quinine
Triamterene

Drugs that may lower your WBC count include:

Antibiotics
Anticonvulsants
Antihistamines
Antithyroid drugs
Arsenicals
Barbiturates
Chemotherapy drugs
Diuretics
Sulfonamides

References

McPherson RA and Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: WB Saunders; 2007:461-2.

Hoffman R, Benz Jr. EJ, Shattil SJ, et al., eds. Hematology: Basic Principles and Practice. 4th ed. Philadelphia, Pa: Churchill Livingston; 2005:2676-77, 2733.

Review Date:3/8/2007
Reviewed By:Mark Levin, MD, Hematologist and Oncologist, Newark, NJ. Review provided by VeriMed Healthcare Network.

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