Blood eosinophilia is defined as peripheral blood eosinophil count > 0.5 × 10 9/L. Blood hypereosinophilia is persistent eosinophil count > 1.5 × 109/L on 2 examinations over ≥ 1 month without evidence of organ damage. Hypereosinophilic syndrome is hypereosinophilia of any cause (reactive or clonal) associated with clear evidence of hypereosinophilia-related organ damage.
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