Airway inflammation is increased in patients with occupational asthma when they are exposed to the agent to which they are allergic. The assessment of airway inflammation can be non-invasively performed by analyzing sputum or, even more easily, by measuring exhaled nitric oxide. Exhaled nitric oxide is a gas produced in the airways that is often increased in patients with asthma and is correlatively associated with airway inflammation. In contrast to sputum eosinophil count, exhaled nitric oxide has been shown to inconsistently increase in patients with occupational asthma after exposure to the agents to which they are allergic. In a study recently published in The Journal of Allergy and Clinical Immunology, C. Lemiere and colleagues aimed to identify groups of subjects with occupational asthma in whom exhaled nitric oxide could be a useful tool in the investigation of occupational asthma.

The authors studied 178 consecutive subjects, who had been investigated for possible occupational asthma by specific-inhalation challenges, which consist in exposing them to the suspected agent in the laboratory. They measured exhaled nitric oxide before and after the exposure to the suspected agent. The statistical analysis identified three subgroups among the 98 subjects who tested positive and thus, had occupational asthma. One group did not show any increase in its exhaled nitric oxide levels. This group of subjects was only exposed to chemicals whereas the two other groups were mainly exposed to proteins; for example, flour, enzymes, and latex. Further analysis uncovered that the type of agent (chemicals vs. proteins) was the only factor associated with an increase in exhaled nitric oxide in subjects with a positive specific-inhalation challenge.

The authors showed that an increase in exhaled nitric oxide after exposure to agents causing occupational asthma seems to occur more consistently in subjects exposed to proteins than in those exposed to chemicals. The measure of exhaled nitric oxide levels is likely to be more useful in the investigation of occupational asthma during the evaluation of patients exposed to protein agents than those exposed to chemicals.