How can I differentiate between allergic and non-allergic causes of eosinophilia in my patients?

To differentiate between allergic and non-allergic causes of eosinophilia in patients, start with a detailed clinical history focusing on exposure to known allergens, presence of atopic conditions (such as asthma, eczema, or allergic rhinitis), and temporal correlation of symptoms with allergen exposure, as allergic eosinophilia typically aligns with these factors NICE CG116. Conduct targeted allergy testing, including skin prick tests or specific IgE assays, to identify sensitisation to common allergens, which supports an allergic cause NICE CG116. In contrast, non-allergic eosinophilia often lacks identifiable allergen triggers and may present with persistent eosinophilia despite negative allergy tests Moneret-Vautrin et al. 1988. Additionally, non-allergic eosinophilic conditions may be associated with other systemic or local inflammatory processes, infections, or drug reactions without an IgE-mediated mechanism Czarnobilska 2005. Laboratory evaluation should include peripheral eosinophil counts and, where relevant, tissue biopsy or nasal cytology to detect eosinophilic infiltration; the pattern of eosinophil activation and cytokine profiles may differ, with allergic eosinophilia showing Th2 cytokine predominance NICE CG116 and non-allergic eosinophilia potentially involving alternative inflammatory pathways Czarnobilska 2005. Thus, integrating clinical history, allergy testing, and laboratory findings allows differentiation, with UK guidelines emphasising allergy testing and clinical correlation as primary tools NICE CG116, while literature highlights the importance of recognising non-allergic eosinophilic inflammation as a distinct entity requiring broader diagnostic consideration Moneret-Vautrin et al. 1988Czarnobilska 2005.