The Diagnostic Value of Delayed-Type Reactions to Perennial Aeroallergens for Atopic Disease

Background: Delayed-type reactions to aeroallergens have been observed, however, their clinical significance continues to be debated. Objective: We assessed the prevalence and significance of delayed-type reactions to aeroallergens in atopic patients. Methods: Retrospective study including 266 patients with history or evidence of atopic disease (atopic dermatitis [AD], allergic rhinitis, and/or allergic asthma) and tested via either the intradermal skin test (IDT) or atopy patch test for common aeroallergens, specifically house dust mites (Dermatophagoides farinae, Dermatophagoides pteronyssinus) and perennial molds (Aspergillus fumigatus, Penicillium notatum). All patients were tested via IDT with both immediate (15 minute) and delayed (2 and 4 days) readings. Delayed reading was considered positive if the IDT injection site demonstrated at least 5mm induration 48 hours after inoculation. Results: In total, 195 (73.3%) patients demonstrated an immediate-type reaction, whereas 118 (44.4%) had a delayed-type reaction. In total, 75 (28.2%) patients experienced both immediate- and delayed-type reactions, 43 (16.2%) reacted delayed-type only, and 85.3% of delayed-type reactions to individual aeroallergens were associated with eczematous lesions predominantly in air-exposed areas. Conclusion: Delayed-type reactions to aeroallergens are prevalent and clinically significant as a component of extrinsic AD and atopic diseases. The data support delayed reading of the IDT to guide diagnosis and management in these patients.