What initial tests should be conducted to determine the underlying cause of eosinophilia in adults?

Initial investigations for eosinophilia in adults should focus on identifying common and treatable causes, integrating clinical history and targeted laboratory tests. A full blood count with differential is essential to confirm eosinophilia and assess for other haematological abnormalities NICE NG245. A detailed travel, occupational, medication, and exposure history is critical to guide further testing, especially for parasitic infections in returning travellers or migrants Checkley et al. 2010. Stool microscopy for ova, cysts, and parasites should be performed to detect helminth infections, which are a common cause of eosinophilia in this group Checkley et al. 2010. Serological tests for specific parasites (e.g., Strongyloides, Schistosoma) may be indicated based on exposure risk Checkley et al. 2010. Screening for allergic diseases, including assessment for asthma or atopic conditions, is recommended as these are frequent non-infectious causes of eosinophilia NICE NG245. Chest X-ray can be useful to identify pulmonary infiltrates suggestive of eosinophilic lung diseases or malignancy NICE NG245. In cases where initial investigations are inconclusive, referral for haematological evaluation including peripheral blood film, immunophenotyping, and possibly bone marrow biopsy may be necessary to exclude haematological malignancies or hypereosinophilic syndromes NICE NG245. Thus, the initial approach combines clinical assessment with targeted laboratory and imaging investigations to identify infectious, allergic, and malignant causes of eosinophilia in adults NICE NG245; Checkley et al. 2010.