Increase in exhaled nitric oxide (eNO) after work-related isocyanate exposure

The objective of this study was to evaluate the role of eNO changes post inhalative isocyanate challenge tests (ΔeNO) with regard to specific asthmatic reactions and unspecific bronchial hyperresponsiveness (BHR) to predict clinical and subclinical responses of isocyanate workers. Methods: 55 workers with isocyanate-related respiratory complaints (29 with BHR and 25 without BHR) underwent occupational-type challenge tests. We determined eNO before, during and up to 22 h after diagnostic isocyanate challenge. Results: The 12 asthmatic responders (22%) in the isocyanate-challenge test showed the highest eNO changes 22 h after challenge as well as a significant association between these changes and BHR. There was a positive association between an eNO increase of >50% and an asthmatic response when compared to nonresponders with an odds ratio of 6.1; 95% CI 1.4–26.3; P=0.02. More than half of the employees with BHR (52%) but only 20% of those without BHR developed an eNO rise of >50% after 22 h. Furthermore, a significant positive association was found between the combination of BHR plus eNO increase of 50% after 22 h and the maximum sR_aw change (% of baseline value) during the period 0–22 h after isocyanate exposure. The combination of BHR and eNO increase of >50% was also associated with clinical symptoms during specific challenge tests (cough, shortness of breath, and/or rhinitis). Discussion and conclusions: An eNO increase 22 h post isocyanate challenge occurred in two-thirds of responders and in approximately half of nonresponders with BHR but only rarely in those without BHR. The combination of BHR and eNO increase in nonresponders may offer a new diagnostic tool to register subjects with an increased risk of developing occupational asthma. However, a large study group to perform follow-up investigations into this topic would be helpful to emphasize the importance of this finding.