Abnoramilities of white blood cells may involve changes in their blood counts, in the normal content of young and mature forms, or emergence of the immature precursors in the peripheral blood. Abnoramilties may also concern the function of leukocytes.
Normally there are from 4 to 9x109 leukocytes/L in the peripheral blood. Disorders of white blood cells may be classified into two broad categories: leukocytosis and leucopenia. The term «leukocytosis» implies an increase in the WBC counts above 9x109/L, while leukopenia means a decrease in WBC below 4x109/L. Various principles of categorization of the WBC disorders are demonstrated in fig. 20.
Leukocytosis and leukopenia are not discrete nozological entities, and they are often used as indices of the extent and course of various pathological processes. Thus, leukocytosis and leukopenia are typical pathological processes.
LEUKOPENIA
The specific types of leukopenia are called neutropenia, lymphopenia, monopenia, eosinopenia, etc., depending on the type of cells involved. Respectively, the specific types of leukocytosis are neutrophilia, lymphocytosis, monocytosis, eosinophilia, or basophilia.
An abnormally low white blood cell count usually results from a reduced number of neutrophils. This state refers to neutropenia or granulocytopenia.
Neutropenia
The obligation of the neutrophil in phagocytic defence of the host is generally met if the neutrophil count is above 1.000 cells/uL. If the neutrophil count drops further, particularly below 500 cells/uL, the incidence of serious,
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Fig. 20
recurrent, and difficult-to-treat infections rises markedly. When there are fewer than 200 cells/uL, the inflammatory process is absent.
Abnormalities in the marrow compartment: bone marrow defects account for the majority of neutropenias in clinical practice. Failure of the marrow compartment can occur as a result of direct injury, in which case the marrow usually contains fewer than normal hematopoietic cells, or from maturation defects of hematopoietic cells, characterized principally by normal or increased numbers of morphologically abnormal hematopoietic cells.