Methacholine responsiveness, respiratory symptoms and pulmonary function in aluminum potroom workers

The relationship between nonspecific bronchial reactivity and work-related asthmatic symptoms was examined in a cross-sectional study of 337 aluminium potroom workers by a shortened method of continuous methacholine nebulization. The provocative concentration producing a 20% fall in forced expiratory volume in one second (FEV1) (PC20) was less than or equal to 8 mg.ml-1 (hyperresponsiveness) in 17 workers (5%), whilst minor responsiveness (8 mg.ml-1 less than PC20 less than 32 mg.ml-1) was present in 24 subjects (7%). The prevalence of work-related asthmatic symptoms was 9%. Female sex, ex-smoker and airflow limitation were significant predictors of methacholine responsiveness (p less than 0.05). In a multiple logistic regression analysis the odds ratios (OR) for work-related asthmatic symptoms was 10.8 (95% confidence interval: 2.9-40.6) for hyperresponsiveness and 4.4 (95% confidence interval: 1.2-16.4) for minor responsiveness. The sensitivity, specificity and predictivity of PC20 less than 32 mg.ml-1 for work-related asthmatic symptoms were 35, 92 and 35%, respectively, whilst the agreement, when adjusted for the by chance expectation, was 0.27 (95% confidence interval: 0.10-0.54). Although a significant association was found between bronchial reactivity and work-related asthmatic symptoms, the usefulness of the methacholine test as a tool for detection of work-related asthmatic symptoms appears to be of limited value due to its low sensitivity.