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 hyperresponsivene ss, 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 yea rs by the ECRHS questionnaire. Total IgE and specific IgE to four inhalant allergens were measured using CAP System. Bronchial hyperresponsiveness (BH R) was defined as PD20 less than or equal to 2 mg methacholine and 'high eo sinophil count' as an eosinophil count in the highest quartile. Results Forty-three percent of the subjects with specific IgE to inhalant a llergens was asymptomatic. These subjects had a lower degree of sensitizati on 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 sensitiz ed to indoor allergens. Low levels of specific IgE to indoor allergens were only associated with symptoms when BHR was present. Sensitization to outdo or allergens was associated with symptoms at all levels of specific IgE, in dependently of BHR or eosinophils. Conclusion Our epidemiological data suggest that whether low levels of spec ific IgE to indoor allergens lead to allergic symptoms is probably determin ed by the concurrent existence of inflammation of the airways.