Association of bronchial reactivity to occupational agents with methacholine reactivity, sputum cells and immunoglobulin E-mediated reactivity.

Background: Bronchial responsiveness and IgE-mediated reactivity are associated with specific bronchial reactivity to allergens.

Objective: Our aim was to examine whether airway inflammation also plays a role.

Methods: Retrospective analysis of all subjects who underwent specific inhalation challenges in the investigation of occupational asthma (OA) since 2000. Responsiveness to methacholine (PC(20) ) and levels of eosinophils and neutrophils in induced sputum on the control day were associated with the presence of OA (positive-specific inhalation challenge). In a sample of subjects exposed to wheat flour, we also examined the role of specific IgE- mediated reactivity (skin reactivity, specific IgE).

Results: PC(20) level was significantly more often normal in subjects with OA (35 of 129, 27% instances) by comparison with non-OA (15 of 189, 8% instances), but the positive predictive value of responsiveness to methacholine for OA was low (35%). Coupling information on the level of eosinophils to responsiveness to methacholine increased positive predictive values for OA from 39% to 69% depending on the thresholds used. The best balance of positive (69%) and negative (60%) predictive values was obtained in the case of normal PC(20) and eosinophils ≥3%. In a multivariate analysis carried out in 34 subjects exposed to wheat flour, responsiveness to methacholine, sputum eosinophils, skin weal size and levels of specific IgE were all significantly associated with OA to wheat flour.

Conclusion And Clinical Relevance: Information on the level of sputum eosinophils in addition to PC(20) provides a better association with OA vs. non-OA when PC(20) is normal. Levels of sputum eosinophils in addition to PC(20) and IgE-mediated reactivity increase the likelihood of OA due to wheat flour.