White Blood Cell Counts

The procedure used to count white blood cells is similar to that used for counting red blood cells. However, before a white blood cell count is made, the red blood cells in the blood sample are destroyed so they will not be mistaken for white blood cells. Normally, a cubic millimeter of blood includes 5,000 to 10,000 white blood cells.

The total number and percentages of different white blood cell types are of clinical interest. A rise in the number of circulating white blood cells may indicate infection. A total number of white blood cells exceeding 10,000 per mm3 of blood constitutes leukocytosis, indicating acute infection, such as appendicitis. Leukocytosis may also follow vigorous exercise, emotional disturbances, or great loss of body fluids.

A total white blood cell count below 5,000 per mm3 of blood is called leukopenia. Such a deficiency may accompany typhoid fever, influenza, measles, mumps, chicken pox, AIDS, or poliomyelitis. Leukopenia may also result from anemia or from lead, arsenic, or mercury poisoning.

A differential white blood cell count (DIFF) lists percentages of the types of leukocytes in a blood sample. This test is useful because the relative proportions of white blood cells may change in particular diseases. The number of neutrophils, for instance, usually increases during bacterial infections, and eosinophils may become more abundant during certain parasitic infections and allergic

(3) Bacteria multiply

(1) Splinter punctures epidermis

(2) Bacteria are introduced into the dermis

(1) Splinter punctures epidermis

(2) Bacteria are introduced into the dermis

Blood vessels

(4) Injured cells release histamine, causing blood vessels to dilate

Blood vessels

(3) Bacteria multiply

(4) Injured cells release histamine, causing blood vessels to dilate

(5) Neutrophils move through (6) Neutrophils destroy blood vessel walls and bacteria by phagocytosis migrate toward bacteria

(5) Neutrophils move through (6) Neutrophils destroy blood vessel walls and bacteria by phagocytosis migrate toward bacteria

Figure 14.15

When bacteria invade the tissues, leukocytes migrate into the region and destroy the microbes by phagocytosis.

Figure 14.15

When bacteria invade the tissues, leukocytes migrate into the region and destroy the microbes by phagocytosis.

White Blood Cell Population Change

Illness

Elevated lymphocytes

Hairy cell leukemia, whooping cough, mononucleosis

Elevated eosinophils

Tapeworm infestation, hookworm infestation, allergic reactions

Elevated monocytes

Typhoid fever, malaria, tuberculosis

Elevated neutrophils

Bacterial infections

Too few helper T cells (lymphocytes)

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