[Leukocytopenia as an incidental finding. Finding the etiology]

Any leukopenia of less than 1000/microliter poses an acute threat to life, and mandates an immediate search for the underlying cause. An extensive history-taking (use of drugs? visits abroad? previous illnesses?) and physical examination (splenomegaly? exanthema? signs of hemorrhage?) are mandatory. In addition to a manual differential blood count, bone marrow aspiration for cytological and histological evaluation must be requested. In this overview, the major differential diagnoses, such as allergic agranulocytosis, leukemia, pernicious illnesses (e.g. malaria), hypersplenic syndrome and a number of infectious diseases are discussed.