Background Some studies have reported that the levels of exhaled nitric oxide (ENO) in asthmatics are similar to those in subjects with allergic rhinitis, and it has been postulated that atopic status might be the determinant of enhanced nitric oxide production in asthma.
Objectives The aim of this study was to determine differences in ENO levels between asthmatics and subjects with allergic rhinitis sensitized to the same allergen, and to correlate these levels with airway responsiveness.
Methods Nineteen patients with asthma and 18 subjects with allergic rhinitis monosensitized to Parietaria pollen were enrolled in the study. ENO values and airway responsiveness to methacholine and adenosine 5′-monophosphate (AMP) were measured during the pollen season. The response to each bronchoconstrictor agent was measured by the provocative concentration required to produce a 20% fall in FEV1 (PC20). ENO was measured with the single-exhalation method.
Results The geometric mean (95% confidence interval) ENO values were significantly higher in asthmatics than in subjects with allergic rhinitis: 72.4 p.p.b. (54.9–93.3 p.p.b) vs. 44.7 p.p.b. (30.9–64.6 p.p.b., P = 0.03). In asthmatics, a significant correlation was found between ENO and PC20 AMP values (ρ = −0.57, P = 0.02), whereas no correlation was detected between ENO and PC20 methacholine (ρ =− 0.35, P = 0.14).
Conclusions Our results suggest that atopy is not the only determinant of increased ENO levels detected in subjects with asthma, and that responsiveness to AMP may be a more sensitive marker for assessing airway inflammation in asthma compared to methacholine.