Fractional Exhaled Nitric Oxide (FeNO) in the Screening and Diagnosis Work-Up of Occupational Asthma

Opinion Statement

FeNO is a simple non-invasive tool used as a surrogate marker of airway inflammation in the management of asthma. FeNO has been assessed in several populations of workers exposed to high- and low-molecular weight agents. However, there are many confounding factors to consider in the interpretation of FeNO. As such, its use in the investigation of occupational asthma (OA) has yielded inconsistent results. In screening studies of OA to high molecular weight (HMW) agents, an increase of FeNO over time has been associated with the development of bronchial hyperresponsiveness (BHR). When used in the investigation of OA, increases in FeNO show high positive predictive values for a positive specific inhalation challenge (SIC) to HMW agents. Subjects with high specific IgE to their workplace allergens seem to present higher increases in FeNO than subjects without specific IgE to causal agent. Changes in FeNO have less frequently been observed in studies of OA to low molecular weight (LMW) agents than OA to HMW agents, except for isocyanate-induced OA. Cluster analyses of patients exposed to various HMW and LMW agents have documented significant increases of FeNO in clusters of patients with OA to HMW agents, but not LMW. Recent studies have provided useful information for improving our understanding of the pathophysiology of exhaled NO in OA despite the previously reported conflicting results. Future studies are still required to clarify its role in the screening, investigation, and management of OA.

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