Allergic sensitization to indoor and outdoor allergens and relevance to bronchial hyperresponsiveness in younger and older subjects

Background: Most previous epidemiological studies on the relationship between allergy and bronchial hyperresponsiveness (BHR) have made no distinction between sensitization to indoor and outdoor allergens. We studied the relationship between specific sensitization to allergen and BHR and further assessed whether this was different in young adults and older subjects. Methods: Specific IgE to indoor allergens (house dust mite and cat) and outdoor allergens (timothy grass and birch) were measured using the CAP System. BHR was defined as PD20 less than or equal to 2 mg methacholine. Multiple logistic regression analysis was performed to study independent relationships between BHR and specific IgE to indoor and outdoor allergens in 1018 young adults (20-44 years) and 909 older subjects (45-70 years). Results: In the older age group specific IgE to indoor allergens was associated with BHR at a lower level (class 2) than in young adults (class greater than or equal to 3). Young adults with multiple sensitization had the highest risk of BHR. Subjects who were exclusively sensitized to pollen did not show increased BHR in both age groups. Total IgE had, independently of sensitization, only a significant dose-response relationship with BHR in the oldest age group. Conclusions: The association between sensitization and BHR is dependent on the nature of the allergen and the level of specific IgE. Furthermore, this study shows for the first time that total IgE is associated with BHR at older ages, independently of sensitization.