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[″ + kytos, cell, + osis, condition]
An increase in the number of leukocytes (usually above 10,000/mm3) in the blood. It occurs most commonly in disease processes involving infection, inflammation, trauma, or stress, but it also can result occasionally from the use of some medications, e.g., corticosteroids.
SEE: leukocyte; SEE: leukopenia
It usually is caused by an increase in one particular type of white blood cell (WBC). For example, neutrophils increase in acute bacterial infections and inflammation, monocytes increase in chronic infections, lymphocytes increase in viral and chronic bacterial infections, and eosinophils increase in allergic disorders, such as asthma. Leukemias often cause a huge increase in circulating cells, owing to the unchecked reproduction of a single clone of malignant cells.

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