White Blood Cell Count And Differential

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White Blood Cell Count And Differential

Below:

• Definition

• Purpose

• Description

• Preparation

• Aftercare

• Key Terms

Definition

The white blood cell count and differential determine the number of

white blood cells and the percentage of each type of white blood cell

in a person's blood. These tests are included in general health

examinations and help investigate a variety of illnesses, including

infection, allergy, and leukemia.

Purpose

The white blood cell count provides a clue to the presence of

illness. White cells protect the body by fighting infection and

attacking foreign material. When extra white cells are needed, the

bone marrow increases production.

There are five types of white cells, each with different functions:

neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The

differential reveals if these cells are present in a normal

distribution, or if one cell type is increased or decreased. This

information helps diagnose specific types of illness.

Conditions or medications that weaken the immune system, such as AIDS

or chemotherapy, cause a decrease in white cells. The white cell

count detects dangerously low numbers of white cells.

Recovery from illness can be monitored by the white cell count.

Counts continuing to rise or fall to abnormal levels indicate a

worsening condition; counts returning to normal indicate improvement.

Description

Neutrophils increase in response to bacterial infection. They destroy

bacteria by enveloping and digesting them, a process called

phagocytosis. When many neutrophils are needed, they are released

from the bone marrow as immature cells, called bands or stab cells.

Lymphocytes fight viral infections and some bacterial infections.

Certain lymphocytes directly attack invading microorganisms; others

produce antibodies that attack and destroy microorganisms and other

foreign material. Large lymphocytes, called atypical lymphocytes, are

seen during infectious mononucleosis and other illnesses.

Monocytes increase during severe infections, and other conditions.

They remove debris and microorganisms by phagocytosis. Eosinophils

and basophils increase in response to allergic reactions and

parasitic infection.

White cell counts are usually done on an automated instrument. A

sample of blood is mixed with a chemical to burst the red blood

cells. The remaining white cells are counted by the instrument.

The differential is done by spreading a drop of blood on a microscope

slide. The slide is stained with a special stain and examined under a

microscope. One-hundred white cells are counted and identified as

either neutrophils, bands, lymphocytes, monocytes, eosinophils or

basophils. Any atypical or immature cells also are counted. Cells are

identified by the shape and appearance of the nucleus, the color of

cytoplasm (the background of the cell), and the presence and color of

granules. The percentage of each cell type is reported. At the same

time, red cells and platelets are examined for abnormalities in

appearance. Some instruments perform an automated differential.

Both the white blood cell count (also called white count or leukocyte

count) and the differential (also called diff) are covered by

insurance. Results are available the same day.

Normal results

Total white cell count 5,000-10,000 uL. Neutrophils 50-60%.

Lymphocytes 20-40%. Monocytes 2-6%. Eosinophils 1-4%. Basophils 0.5-

1%. Bands 0-3%.

Abnormal results

The white cell count and differential are interpreted according to a

person's clinical condition and medical history. Leukocytosis (a

white count increased to over 10,000/uL) is seen in bacterial

infections, inflammation, leukemia, trauma, and stress. Leukopenia (a

white count decreased to less than 4,000/L) is seen in some viral

infections or severe bacterial infections, and conditions that affect

the bone marrow such as dietary deficiencies, chemotherapy, radiation

therapy, and autoimmune diseases.