WBC count

WBC count

Definition:

A test to measure the number of white blood cells (WBCs) in blood; almost always ordered as part of the CBC (complete blood count). See also blood differential.

Alternative Names:

Leukocyte count; White blood cell count

How the test is performed:

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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.

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.

How to prepare for the test:

Adults:
No special preparation is necessary.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

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:

To measure the number of white blood cells in the blood. White blood cells are the major infection-fighting cells in the body, and are also involved in reactions to other challenges such as allergies, tumors, and stress in general. This assessment is important in many different conditions and disease states.

Normal Values:

WBC: 4,500 to 10,000 cells/mcl

Note: cells/mcl = cells per microliter

What abnormal results mean:

Low numbers of WBCs (leukopenia) may indicate:

bone marrow failure (for example, due to infection, tumor, fibrosis)
presence of cytotoxic substance
collagen-vascular diseases (such as lupus erythematosus)
disease of the liver or spleen
radiation

High numbers of WBCs (leukocytosis) may indicate:

infectious diseases
inflammatory disease (such as rheumatoid arthritis or allergy)
leukemia
severe emotional or physical stress
tissue damage (for example, burns)

This test may be performed under many conditions and in many disease states.

What the risks are:

Risks associated with venipuncture are slight:

excessive bleeding
fainting or feeling light-headed
hematoma (blood accumulating under the skin)
infection (a slight risk any time the skin is broken)
multiple punctures to locate veins

Special considerations:

There are various 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 acute stress will result in an increased production of WBCs. This usually entails increased numbers of cells and an increase in the percentage of immature cells (mainly band cells) in the blood. This change is referred to as a "shift to the left".

Interfering factors:
Acute emotional or physical stress can increase WBC counts.

People who have had a splenectomy have a persistent mild elevation of WBCs.

Drugs that may increase WBC counts include epinephrine, allopurinol, aspirin, chloroform, heparin, quinine, corticosteroids, and triamterene.

Drugs that may decrease WBC counts include antibiotics, anticonvulsants, antihistamine, antithyroid drugs, arsenicals, barbiturates, chemotherapeutic agents, diuretics, and sulfonamides.

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.

Review Date: 11/18/2001
Reviewed By: Rebecca Elstrom, M.D., Division of Hematology-Oncology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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