FeNO as a predictor of asthma control improvement after starting inhaled steroid treatment

• Intermediate FeNO levels (25–50 ppb) are regarded cautiously in asthma management.
• Subjects with intermediate and high FeNO improved similarly in asthma control.
• Subjects with low FeNO levels achieved asthma control to a very low extent.
• The value of intermediate FeNO levels in asthma management should be reappraised.

IntroductionThe fraction of NO in exhaled air (FeNO) is a marker of inflammation in asthma. The aim of the present study was to assess, in a real-world setting, whether only high (⩾50 ppb) FeNO levels predict improvement in asthma control when being treated with inhaled corticosteroids (ICS), as suggested by current guidelines on the clinical use of FeNO.MethodsFeNO and asthma control were assessed in a retrospective observational study in 153 non-smoking, steroid-naïve, adult subjects with asthma with a mean age of 40 years both before and after 6 weeks (median follow-up time) of treatment with 500 μg beclomethasone (median).ResultsHaving at the initial visit intermediate FeNO (⩾25 and <50 ppb) and high FeNO (⩾50 ppb), compared to normal FeNO (<25 ppb), were associated with a larger proportion of subjects achieving an improvement of Asthma Control Questionnaire (ACQ) score with ⩾1 (78% and 67% vs 43%, p < 0.05) or both ⩾1 improvement and asthma control at follow-up (31% and 37% vs 4%, p < 0.05). These associations were consistent in multiple logistic regression models after adjustments for confounders.ConclusionsIt is not only high but also intermediate FeNO levels that are associated with a significant improvement in asthma control after starting ICS treatment. This challenges current clinical guidelines stating that only high FeNO levels predict response to ICS treatment.