Occupational Asthma Reference

Pralong JA, Lemière C, Rochat T, L'Archevêque J, Labrecque M, Cartier A, Predictive value of nonspecific bronchial responsiveness in occupational asthma, J Allergy Clin Immunol, 2016;137:412-416,http://dx.doi.org/10.1016/j.jaci.2015.06.026
(Plain text: Pralong JA, Lemiere C, Rochat T, L'Archeveque J, Labrecque M, Cartier A, Predictive value of nonspecific bronchial responsiveness in occupational asthma, J Allergy Clin Immunol)

Keywords: Canada, bronchial reactivity, oa, challenge

Known Authors

André Cartier, Hôpital de Sacré Coeur, Montreal, Quebec, Canada André Cartier

Manon Labrecque, Hôpital de Sacre Coeur, Montreal, Quebec, Canada Manon Labrecque

Catherine Lemière, Hôpital de Sacré Coeur, Montreal, Quebec, Canada Catherine Lemière

T Rochat, Geneva T Rochat

Jacques Pralong, Sacre Coeur, Montreal Jacques Pralong

Jaques Pralong, Jaques Pralong

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Abstract

Background
The diagnosis of occupational asthma (OA) can be challenging and needs a stepwise approach. However, the predictive value of the methacholine challenge has never been addressed specifically in this context.

Objective
We sought to evaluate the sensitivity, specificity, and positive and negative predictive values of the methacholine challenge in OA.

Methods
A Canadian database was used to review 1012 cases of workers referred for a suspicion of OA between 1983 and 2011 and having had a specific inhalation challenge. We calculated the sensitivity, specificity, and positive and negative predictive values of methacholine challenges at baseline of the specific inhalation challenge, at the workplace, and outside work.

Results

At baseline, the methacholine challenge showed an overall sensitivity of 80.2% and a specificity of 47.1%, with positive and negative predictive values of 36.5% and 86.3%, respectively. Among the 430 subjects who were still working, the baseline measures displayed a sensitivity of 95.4%, a specificity of 40.1%, and positive and negative predictive values of 41.1% and 95.2%, respectively. Among the 582 subjects tested outside work, the baseline measures demonstrated a sensitivity and specificity of 66.7% and 52%, respectively, and positive and negative predictive values of 31.9% and 82.2%, respectively. When considering all subjects tested by a methacholine challenge at least once while at work (479), the sensitivity, specificity, and positive and negative predictive values were 98.1%, 39.1%, and 44.0% and 97.7%, respectively.

Conclusion
A negative methacholine challenge in a patient still exposed to the causative agent at work makes the diagnosis of OA very unlikely.

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Associated Questions

Registered users of this website have associated this reference with the following questions. This association is not a part of the BOHRF occupational asthma guidelines.

What are the sensitivity and the specificity of changes in non-specific reactivity at work and away from work in the diagnosis of validated cases of occupational asthma?
burgeps This study reports a a very high sensitivity for non-specific reactivity in predicting a positive specific challenge test to an occupational agent. Most of those with negative NSBR were away from exposure at the time of the test, something generally found by others. The high sensitivity is partly explained by using a higher cut-off for normality (16mg/ml) than the usual 8mg/ml, but this is still unlikely to explain the very high sensitivity found. We need assurance that NSBR was not used to decide who should have a specific challenge (this is recommended in some guidelines). Another possible explanation is the high prevalence of the eosinophilic phenotype, something associated with NSBR. Others have found much lower sensitivities for NSBR in predicting the response to specific challenges, particular in those without sputum eosinophilia. The specificities quoted depend on the controls selected (or in this case those with negative specific challenges) as NSBR cannot separate occupational from non-occupational asthma.

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