Diagnostic Algorithm in patients with Eosinophilia. In a first step, the presence of eosinophilia or hypereosinophilia (HE) is confirmed. Then, the etiology of eosinophilia/HE is studied, and the patient is examined for the presence of HE-related organ damage. Based on results, patients are classified into various hematologic or immunologic diseases. In those who are suffering from HE-related organopathy, the additional diagnosis of hypereosinophilic syndrome (HES) is established. In a small proportion of cases, familial HES or rare syndromes presenting with HE, such as the Gleich syndrome or Churg Strauss syndrome (CSS), are diagnosed. L-HES, lymphoid variant HES; EMS, eosinophilia myalgia syndrome.