Health Encyclopedia

Blood differential

Definition

The blood differential test measures the percentage of each type of white blood cell (WBC) that you have in your blood. It also reveals if there are any abnormal or immature cells.

Alternative Names

Differential; White blood cell differential count

How the test is performed

The health care provider will take blood from your vein. The blood collects into an airtight container.

In infants or a young child, blood will be taken from a heel stick or finger stick. The blood is collected in a small glass tube or onto a slide or test strip.

Cotton or a bandage may be applied to stop any bleeding.

A laboratory specialist takes a drop of blood from your sample and smears it onto a glass slide. The smear is stained with a special dye, which helps tell the difference between various types of white blood cells.

Five types of white blood cells, also called leukocytes, normally appear in the blood:

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

A computer or the health care provider counts the number of each type of cell. The test shows if the number of cells are in proper proportion with one another, and if there is more or less of one cell type.

How to prepare for the test

No special preparation is necessary.

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

This test is done to diagnose an infection, anemia, and leukemia. It may also be used to see if treatment for any of these conditions is working.

Normal Values

Neutrophils: 40% to 60%
Lymphocytes: 20% to 40%
Monocytes: 2% to 8%
Eosinophils: 1% to 4%
Basophils: 0.5% to 1%
Band: 0% to 3%

What abnormal results mean

Any infection or acute stress increases your number of white blood cells. High white blood cell counts may be due to inflammation, an immune response, or blood diseases such as leukemia.

It is important to realize that an abnormal increase in one type of white blood cell can cause a decrease in the percentage of other types of white blood cells.

An increased percentage of neutrophils may be due to:

A decreased percentage of neutrophils may be due to:

Aplastic anemia
Chemotherapy
Influenza
Widespread bacterial infection
Radiation therapy

An increased percentage of lymphocytes may be due to:

Chronic bacterial infection
Infectious hepatitis
Infectious mononucleosis
Lymphocytic leukemia
Multiple myeloma
Viral infection (such as infectious mononucleosis, mumps, measles)
Recovery from a bacterial infection

A decreased percentage of lymphocytes may be due to:

Chemotherapy
HIV infection
Leukemia
Radiation therapy
Sepsis

An increased percentage of monocytes may be due to:

Chronic inflammatory disease
Parasitic infection
Tuberculosis
Viral infection (for example, infectious mononucleosis, mumps, measles)

An increased percentage of eosinophils may be due to:

Allergic reaction
Parasitic infection
Hodgkin's disease

A decreased percentage of basophils may be due to:

Acute allergic reaction

What the risks are

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

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.

References

Hoffman R, Benz EJ, Shattil SS, et al. Hematology: Basic Principles and Practice. 4th ed. Orlando, Fl: Churchill Livingstone; 2005:1126.

Noble J. Textbook of Primary Care Medicine. 3rd ed. St. Louis, Mo: Mosby; 2001.

Review Date:3/9/2007
Reviewed By:Mark Levin, MD, Hematologist and Oncologist, Newark, NJ. Review provided by VeriMed Healthcare Network.

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