FACTORS ASSOCIATED WITH INCREASED BRONCHIAL RESPONSIVENESS IN ADOLESCENTS AND YOUNG-ADULTS - THE IMPORTANCE OF ADJUSTMENT FOR PRECHALLENGE FEV(1)

Background: Asymptomatic increased bronchial responsiveness (BR) appea rs to be a major risk factor for later development of asthma, but risk factors for increased BR are not well established. Objective: The rel ationship of age, gender, house dust mite allergy, number of blood eos inophils, and FEV(1) to the degree of nonspecific BR was studied in a population sample of 665 adolescents and young adults, aged 13 to 23 y ears. Methods: Case history, especially concerning smoking habits and respiratory symptoms, was obtained by interview and a self-administere d questionnaire. Pulmonary function, number of blood eosinophils, BR t o inhaled histamine, and skin test reactivity to house dust mites were measured with standard techniques. BR was analyzed as both a continuo us variable (dose-response slope) and a categorical variable (cutoff: PC20 16 mg/ml). Results: Increasing number of blood eosinophils, sensi tivity to house dust mite, and former or current symptoms of asthma we re associated with increasing levels of BR, independently the level of FEV(1). Adjustment for prechallenge FEV(1) revealed a strong associat ion between lower prechallenge FEV(1) and increasing level of BR (p < 0.0001), whereas the previously observed association between female ge nder and higher level of BR vanished. Repeating the analyses after exc lusion of subjects with former or current asthma (n = 85) showed an un changed relationship between house dust mite allergy and level of BR w hether or not prechallenge FEV(1) was included in the regression model , whereas gender only influenced the level of BR when no adjustment wa s made for prechallenge FEV(1). On the contrary, the number of blood e osinophils was only significantly associated with BR after adjustment for baseline FEV(1). Comparable findings were patients with former or current symptoms of asthma and subjects with a prechallenge FEV(1) les s than 80% of predicted value (n = 46) were excluded from the analyses . Conclusion: This analysis suggests that adjustment for prechallenge level of FEV(1) should be considered in studies concerned with risk fa ctors for symptomatic and asymptomatic bronchial hyperresponsiveness.