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White Blood Cell Count (WBC)

A white blood cell (WBC) count, also called a leukocyte count, is part of a complete blood count. It indicates the number of white cells in a micro liter (u1, or cubic millimeter) of whole blood.

WBC counts may vary by as much as 2,000 on any given day, due to strenuous exercise, stress, or digestion. The WBC count may increase or decrease significantly in certain diseases, but is diagnostically useful only when the patient's white cell differential and clinical status are considered

Purpose

• To determine infection or inflammation
• To determine the need for further tests, such as the WBC differential or bone marrow biopsy
• To monitor response to chemotherapy or radiation therapy

Patient preparation

• Explain to the patient that the test is used to detect an infection or inflammation.
• Tell him that a blood sample will be taken. Explain who will perform the venipuncture and when.
• Reassure him that drawing a blood sample will take less than 3 minutes.
• Explain that he may feel slight discomfort from the tourniquet pressure and the needle puncture.
• Inform the patient that he should avoid strenuous exercise for 24 hours before the test. Also tell him that he should avoid ingesting a heavy meal before the test.
• If the patient is being treated for an infection, advise him that this test will be repeated to monitor his progress.
• Review the patient's medication his­tory for drugs that may affect test results, including antineoplastics, antiinfectives, anticonvulsants, thyroid hormone antagonists, and nonsteroidal anti-inflammatory drugs (NSAIDs). Note the use of such medications on the laboratory slip.

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-mllavender-top tube.
• If a hematoma develops at the venipuncture site, apply warm soaks.
• Tell the patient that he may resume normal activity that was discontinued before the test.
• A patient with severe leukopenia may have little or no resistance to infection and requires protective isolation.

Precautions

• Completely fill the sample collection tube, and invert it gently several times to mix the sample and the anticoagulant.

Reference values

The WBC count ranges from 4,000 to 10,000/u1.

Abnormal findings

An elevated WBC count (leukocytosis) often signals infection, such as an abscess, meningitis, appendicitis, or tonsillitis. A high count may also result from leukemia and tissue necrosis due to burns, myocardial infarction, or gangrene

A low WBC count (leukopenia) indicates. bone marrow depression that may result from viral infections or from reactions, such as those following treatment with antineoplastics, ingestion of mercury or other heavy metals, or exposure to benzene or arsenicals. Leukopenia characteristically accompanies influenza, typhoid fever, measles, infectious hepatitis, mononucleosis and rubella.

• Hemolysis due to rough handling of the sample.
• Exercise, stress, or digestion.
• Most antineoplastics; anti-infectives, such as metronidazole and flucytosine; anticonvulsants, such as phenytoin derivatives; thyroid hormone antagonists; and NSAlDs such as indomethacin decrease.

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