LAUSR

Blood eosinophilia remains a common finding in the general population, whereas hypereosinophilia (HE) is extremely rare. Different non‐hematologic and hematologic disorders may be accompanied by blood eosinophilia. Clinical manifestations of eosinophilia‐related disorders range from mild to life‐threatening. Given the various symptoms, a comprehensive approach and close multidisciplinary cooperation are strongly recommended. Hypereosinophilic syndromes (HES) encompass a complex group of disorders defined as persistent peripheral blood HE ≥ 1500/mm3 and end‐organ damage. An initial step in a diagnostic algorithm of HE includes the evaluation of secondary, potentially easy‐to‐treat causes. This HES variant is called reactive and often remains beyond the interest of hematologists. The further evaluation for primary causes of HE relies on a combination of different specialized tests, which are mostly available in hematologic centers and include most of all morphologic assessments of peripheral blood and bone marrow, cytogenetics, and molecular studies. Using these sophisticated methods, one can diagnose the specific HES subtypes based on genetic findings and categorize them according to currently applicable classifications. The choice of therapy differs between HES variants, ranging from corticosteroids and anti‐interleukin‐5 monoclonal antibodies for not‐molecularly defined variants to oral molecules directed against molecular targets. This review presents eosinophilia‐related disorders from a hematologic perspective.