[The evaluation of a patient with eosinophilia]

Eosinophilia is a common laboratory finding with a broad differential diagnosis. Eosinophilia can be classified as primary, secondary, or idiopathic hypereosinophilic syndrome (HES). Primary eosinophilia results from a clonal disorder of eosinophils, while secondary eosinophilia is reactive to a variety of underlying conditions, such as allergic diseases, infections, and drug reactions. Idiopathic HES is a diagnosis of exclusion in patients with persistent hypereosinophilia and end-organ damage without an identifiable cause. The diagnostic workup should focus on identifying the cause and assessing for end-organ damage. The initial evaluation should include a detailed history and physical examination, and laboratory tests to assess for organ involvement. Further testing may be necessary based on the clinical presentation and laboratory findings. The treatment depends on the cause. In cases of secondary eosinophilia, treatment should be directed at the underlying condition.