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Eosinophilia is defined as an absolute eosinophil count >500 cells/μL and requires systematic evaluation to identify underlying causes ranging from allergic reactions to parasitic infections to hematologic malignancies. The workup involves a comprehensive history, physical examination, and targeted laboratory studies based on clinical presentation and severity of eosinophilia.
Eosinophils are granulocytes that play key roles in allergic responses, parasitic infections, and tissue remodeling through release of cytotoxic granule proteins and inflammatory mediators. Eosinophilia results from increased production (IL-5 stimulation), decreased apoptosis, or enhanced tissue recruitment, with causes including HELM conditions (Hematologic, Environmental/drug, Lung disease, Miscellaneous), parasitic infections, and primary eosinophilic disorders.
The diagnostic approach stratifies patients by degree of eosinophilia (mild 500-1,500, moderate 1,500-5,000, severe >5,000 cells/μL) and associated symptoms, with mild cases often representing allergic or drug reactions while severe cases require urgent evaluation for hypereosinophilic syndrome or hematologic malignancy. Initial workup includes complete blood count with differential, comprehensive metabolic panel, stool examination for parasites, and chest imaging, with additional testing guided by clinical findings such as tissue biopsy, bone marrow examination, or molecular studies for clonal eosinophilia.