White-Blood-Cell Count (Leukocyte Count; WBC Count)

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Category: Hematology.
Subcategory: White-blood-cell tests.
Material studied: Blood.
Estimated cost of test: $5.50.
Patient time for test: 5-10 minutes.
Reliability of test results: Good.
Available as home self-test? No.

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BEFORE THE TEST

Purpose of test:

• Suggests presence of infection or inflammation.
• Determines need for further tests, such as the white-blood-cell differential or bone-marrow biopsy.
• Monitors response to chemotherapy or radiation therapy.

Where is test performed?

• Commercial laboratory, hospital, doctor's office.

Who performs test?

• Lab technician, nurse, doctor.

Risks and precautions:

• If tourniquet is applied on the arm too long (over 1 minute), it may cause an inaccurate test result. Request another sample to be collected to ensure accuracy.

Patient preparation:

• Activity - Avoid any strenuous exercise 24 hours before the test.
• Diet - Do not eat a heavy meal before the test.
• Medicines - Inform the person performing the test if you have recently taken any medications listed under Taking these drugs may affect test results. You may be asked not to take this medication before the test.
• Disrobing - None required. Roll up sleeve only.

THE TEST

Sensory factors:

• Touching - You will feel mild discomfort when the needle is inserted into the vein or when the lancet pricks a finger, heel or ear lobe.
• Seeing - You will see the technician, nurse or doctor, the basket or tray to hold the equipment, the needles, syringes, collecting tubes and bandages.
• Feeling - Some degree of apprehension or fear is normal and should be expected. Discomfort disappears when the test is finished.
• Other senses (taste, smell, hearing) - Not affected.

Equipment used:

• Needles, syringes and heparinized collecting tubes. Sterile, disposable equipment prevents contamination or spread of infection. There is no risk of becoming infected with the hepatitis virus, AIDS virus or any other infecting germ.

Description of test:

• Technician, doctor or nurse applies a tourniquet or blood-pressure cuff to the upper arm if blood is collected from a vein.
• Skin over the vein to be stuck is cleaned with alcohol or other antiseptic on a piece of cotton.
• When blood is drawn from a vein, the operator feels the vein to be used then punctures both the skin and vein in one quick stroke. The needle used is a sterile, disposable needle attached to a sterile, disposable syringe.
• Operator withdraws the needle and transfers sample from the collecting syringe into sterile tubes (identified with your name) before sending samples to the laboratory for analysis. Tubes are treated with an anti-coagulant chemical to prevent clotting.
• If blood is collected from a finger, heel or ear lobe, skin over the selected site is cleaned with an antiseptic. The operator quickly pierces the skin to a shallow depth, using a sterile, disposable metal lancet. The drop or two of blood produced is collected into a capillary pipette.

AFTER THE TEST

Immediate post-test care:

• Apply pressure to the puncture site with cotton provided by the laboratory.
• If a vein has been punctured, raise your entire arm over your head while applying pressure.
• Some discoloration, soreness or swelling may develop at the venepuncture site. This responds well to moist, warm compresses applied every 2 to 4 hours.

Activity after test:

• Resume taking any medications that were withheld before the test.
• Resume normal diet.
• Return to pretest activities right away.
• If you have a severe decrease in the number of white blood cells, you may have little or no resistance to infection. This requires special precautions to prevent acquiring infections.

Time before test results available:

• Test requires only a few minutes in the laboratory. Time before results are reported to the doctor or patient varies from a few minutes to a few days.

TEST RESULTS

Test values:

• Values are frequently considered along with a white-blood-cell-differential test or as a part of a complete blood count (CBC).

Normal values:

• WBC count - 4,100 to 10,900/ul.

What HIGH or INCREASED may indicate:

• Infection by most bacteria.
• Leukemia.
• Death of tissue, such as in burns, myocardial infarction or gangrene.

What LOW or DECREASED may indicate:

• Bone-marrow depression from viral infections, such as influenza, red measles or hepatitis.
• Toxic reactions to anti-cancer drugs.
• Toxic reactions from ingesting mercury, gold or other heavy metals.
• Toxic reactions from ingesting benzene or arsenic.
• Typhoid fever.
• Infectious mononucleosis.

Taking these drugs may affect test results:

• Anti-convulsives.
• Anti-infectives.
• Anti-neoplastic agents.
• Flucytosine.
• Indomethacin.
• Metronidazone.
• Non-steroidal anti-inflammatories.
• Phenytoin derivatives.
• Thyroid-hormone antagonists.

Other factors that may affect test results:

• Exercise.
• Stress.
• Digestion.
• Failure to follow dietary restrictions.

From the Complete Guide to Medical Tests by H. Winter Griffith, M.D. © 1988 by Fisher Books; electronic rights by Medical Data Exchange.