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an increase in the absolute number of leukocytes in the peripheral blood.
Physiological leukocytosis occurs after eating and physical exertion. Symptomatic pathological leukocytosis develops with suppurative and inflammatory processes and with a number of infectious diseases, whether produced by specific causative agents of infection or as a result of the bone-marrow reaction to the breakdown of tissues caused by toxic agents or circulatory disorders (for example, myocardial infarction). Transient leukocytosis may result from the release of leukocytes into the blood from bone marrow or other tissues (for example, in stress). In all cases, the leukocytosis is reactive and disappears when its cause disappears. Leukocytosis may be produced by a malignant proliferation of hematopoietic tissue, as in leukemia.