[Differential diagnosis of hypereosinophilia]

Eosinophilia is defined as an elevated absolute number of eosinophilic leukocytes in peripheral blood or tissue. Its absolute number also defines the grade of eosinophilia. The main causes are allergic (including drug side effects) and infectious triggers but malignant and autoimmune diseases can also result in eosinophilia. Severe eosinophilia with the number of eosinophils >5000/µl are mostly caused by myeloproliferative disorders, eosinophilic granulomatosis with polyangiitis or during tissue migration in parasitic tissue infections. Hypereosinophilic syndrome is defined as eosinophilia with >1500 eosinophils/µl and a duration of more than 6 months by exclusion of parasitic infections, allergies or other causes of tissue eosinophilia with end-organ damage. For the diagnosis of a persistent eosinophilia a detailed medical history and physical examination should be followed by early organ screening, infection diagnostics especially for helminth infections and hematological laboratory analyses including bone marrow investigations.