The association of sensitization to inhalant allergens with allergy symptoms: the influence of bronchial hyperresponsiveness and blood eosinophil count

Background We investigated whether the association of allergy symptoms with sensitization to inhalant allergens depends on bronchial hyperresponsiveness, blood eosinophil count, or the degree and nature of sensitization. Methods Data on asthma and rhino-conjunctivitis symptoms were obtained from 1904 subjects from a random sample of the Dutch population, aged 20-70 years by the ECRHS questionnaire. Total IgE and specific IgE to four inhalant allergens were measured using CAP System. Bronchial hyperresponsiveness (BHR) was defined as PD20 less than or equal to 2 mg methacholine and 'high eosinophil count' as an eosinophil count in the highest quartile. Results Forty-three percent of the subjects with specific IgE to inhalant allergens was asymptomatic. These subjects had a lower degree of sensitization than symptomatic sensitized subjects and had 'normal' prevalences of BHR and 'high eosinophil count'. Logistic regression showed that the presence of BHR increased the risk of having symptoms for subjects who were sensitized to indoor allergens. Low levels of specific IgE to indoor allergens were only associated with symptoms when BHR was present. Sensitization to outdoor allergens was associated with symptoms at all levels of specific IgE, independently of BHR or eosinophils. Conclusion Our epidemiological data suggest that whether low levels of specific IgE to indoor allergens lead to allergic symptoms is probably determined by the concurrent existence of inflammation of the airways.