• Catherine Lemiere, Sebastien NGuyen, Francesco Sava, Vinciane D'Alpaos, François Huaux, and Olivier Vandenplas.
• Hôpital du Sacré-Cœur de Montréal, Université de Montréal, Montreal, Quebec, Canada. Electronic address: catherine.lemiere@umontreal.ca.
• J. Allergy Clin. Immunol. 2014 Nov 1; 134 (5): 1063-7.

BackgroundThe added value of fractional exhaled nitric oxide (Feno) remains controversial in the investigation of occupational asthma (OA).ObjectiveWe sought to assess whether or not the increase of Feno levels following positive specific inhalation challenge (SIC) was restricted to phenotypes of subjects sharing common clinical characteristics by using a statistical cluster analysis.MethodsSubjects were investigated for possible OA in a tertiary center using SICs from 2006 to 2012. Feno levels and sputum eosinophil counts were assessed at baseline and 24 hours after SIC. We performed a 2-step cluster analysis of the subgroup of subjects with OA. A multivariate logistic regression was performed in order to identify the variables associated with an increase in Feno in subjects with OA.ResultsOne hundred and seventy-eight subjects underwent SIC; 98 had a positive test. The cluster analysis performed in the OA subgroup identified 3 clusters. Despite a positive SIC, there was no increase in the Feno levels after exposure to occupational agents in Cluster 3, in which subjects were only exposed to low-molecular-weight (LMW) agents. The molecular weight of the agent (high molecular weight vs LMW) was the only factor associated with an increase in Feno (OR: 4.2 [1.1-16.8]) in subjects with a positive SIC.ConclusionAn increase in Feno after exposure to agents causing OA seems to occur more consistently in subjects with OA caused by high molecular weight than in those with OA due to LMW.Copyright © 2014 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.

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