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Definition

noun, plural: leucocytoses

An abnormal increase in white blood cell count in the blood.

Supplement

Leucocytosis is not a disease but a laboratory finding that indicates possible infection since increase in the number of white blood cells could mean heightened immune activity against pathogens.

The normal adult human leucocyte count in the peripheral blood is 4.4-10.8 x 10 ⁹/L. Thus, a white blood count of 11.0 x 10 ⁹/L or more suggests leucocytosis.

Word origin: leucocyte + Greek -osis (an increase, a condition).
Related forms: leucocytotic (adjective)

Variant: leukocytosis

Compare: leucopenia, erythrocytosis.
See also: neutrophilia, lymphocytosis, monocytosis, eosinophilia, basophilia.