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The peripheral blood contains white blood cells of several types in numbers and proportions that vary between quite narrow limits in health but more widely in disease.

Normal White Blood Count & Differential

As with many biologic parameters, there is no strict definition of normal; however, normal ranges are established by laboratories for their population group. Table 26-1 shows a typical set of normal laboratory values for the United States.

Table 26–1. White Blood Cell Count (WBC), Differential: Normal Values.

Variations in these parameters, along with changes in leukocyte morphology as seen in blood smears, are important indicators of disease (Table 26-2).

Table 26–2. Broad Categories of Variation in Leukocyte Number and Morphology. 1

Abnormalities in Lymphocyte Count

Lymphocyte and monocyte origin and function have been considered with the immune system (Chapter 4: The Immune Response).

Lymphocytosis—increased lymphocyte count in peripheral blood—is best considered in relationship to other lymphoproliferative diseases (Chapter 28: The Lymphoid System: I. Structure & Function; Infections & Reactive Proliferations). It may occur as (1) an acute immune response, with many activated or transformed lymphocytes circulating in the blood; (2) a chronic immune response, in which most of the circulating lymphocytes resemble resting small lymphocytes; or (3) neoplastic proliferation (Table 26-3).

Table 26–3. Variation in Lymphocyte Parameters in Peripheral Blood.

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