[Leucocytosis: etiology and diagnostic approach]

Leucocytosis is frequently diagnosed in clinical practice. The first step in the diagnostic approach should be based on differentiation of the leucocyte subpopulations. Neutrophilic leucocytosis can be observed physiologically after physical or mental stress. Furthermore, almost all immune reactions due to infection, allergy or autoimmune diseases are associated with changes in the leucocyte populations. An elevation of white blood cells caused by acute or chronic leukemia, or malignant lymphoma is less frequent. For the diagnosis of hematological malignancies, bone marrow examinations and genetic analyses are necessary.