[Leukocytosis as an incidental finding. Clues in the blood picture]

An increase in the number of leukocytes is often an early pathological signal that may be seen during the course of numerous diseases. Leukocytosis on its own in the absence of clinical symptoms is highly unspecific. If exogenous influences have been excluded, and if laboratory investigations repeatedly indicate leukocytosis, a differentiation must be made between a reactive and a malignant cell proliferation. In addition to the patient's history and clinical findings, a differential blood count is mandatory. Of differential diagnostic significance, is the extent of the left shift. For the qualitative interpretation of the differential blood count, careful microscopic assessment of a blood smear is required. Should atypical cells be found, further diagnostic measures must be initiated without delay, in a center with appropriate facilities.