Occupational Asthma Without Nonspecific Bronchial Hyperresponsiveness.

Abstract

The absence of nonspecific bronchial hyperresponsiveness (NSBH) has been documented in a substantial proportion of workers with occupational asthma (OA). To investigate the clinical and inflammatory characteristics associated with the absence of baseline NSBH in a cohort of subjects with OA ascertained by a positive specific inhalation challenge (SIC). A retrospective study was conducted among 1068 subjects who completed an SIC with various occupational agents at 3 tertiary centers. Among 377 subjects with a positive SIC, 63 (16.7%) did not exhibit baseline NSBH. On postchallenge assessment of these 63 subjects, 45 developed NSBH, whereas 18 still lacked demonstrable NSBH. Multivariate analysis revealed that quiescent asthma-defined by untreated asthma associated with the absence of airway obstruction-was the predominant clinical feature associated with undetectable NSBH at baseline (odds ratio, 3.59; 95% CI, 1.86-6.93). Subjects with and without baseline NSBH exhibited similar rates of postchallenge increases greater than or equal to 13 parts per billion in fractional exhaled nitric oxide (47.8% and 43.6%, respectively) and 2% or higher in sputum eosinophil count (72.2% and 74.2%, respectively). Baseline NSBH assessment identified positive SICs with a substantially lower sensitivity (68%) and negative predictive value (71%) among subjects with quiescent asthma (n = 211) than among those (n = 857) with active disease (87% and 88%, respectively). The absence of NSBH does not allow OA to be ruled out without further investigation in subjects with quiescent asthma. However, a negative NSBH test result has a high negative predictive value for OA among subjects with active disease.