AB040. Determinants of increase FeNO in individuals with suspected asthma

Background: Airway inflammation is the fundamental mechanism in asthma and can be measured non-invasively by means of fractional exhaled nitric oxide (FeNO). Both, The National Institute for Health and Care Excellence (NICE) diagnostics guidance 12 and British guideline on the management of asthma, are recommending the inclusion of FeNO testing as part of diagnosis in patients that have an intermediate probability of having asthma. Furthermore, FeNO testing is recommended as an option for monitoring response to corticosteroid treatment in patients with increased FeNO. However, there is a need for establishing routine data predictors for individuals with increased FeNO, to identify those that would benefit from FeNO measurement as a tool for aiding asthma diagnosis and monitoring treatment responsiveness. To provide a real-life predictive model for the identification of individuals at risk of asthma that have increased FeNO.

Methods: An analysis of real-life standard care and FeNO data derived from a randomised, multi-centre, double-blind, placebo-controlled study entitled: ‘The evaluation of FeNO for predicting response to an inhaled corticosteroid in subjects with non-specific respiratory symptoms’ was carried out. Data from study participants with non-specific respiratory symptoms and an Asthma Control Questionnaire (ACQ) score ≥1 were analysed cross-sectionally. Logistic regression was used to investigate the relationship between FeNO levels, categorised in normal (≤25 ppb) and intermediate (>25 and <40 ppb)/high (≥40 ppb), and a number of determinants, including demographic variables, smoking status, history of atopy, number of short acting beta agonist (SABA) inhalers in the year preceding study participation, symptoms of cough, wheeze and dyspnoea, prior history of oral steroid use, blood eosinophil count (cut off 0.2×10⁹/L) and forced expiratory volume in the first second percent predicted (FEV1% pred).

Results: Overall, 90 individuals were assessed, with a mean ± standard deviation (SD) age of 46±17.1, 50 (56%) were female, and 59 (67%) were non-smokers. Sixty individuals (67%) had normal FeNO levels compared to 30 (33%) with intermediate/high levels. From univariate analyses, the odds ratio (OR) and 95% confidence interval (CI) of being in the intermediate/high FeNO group were increased if individuals were male [4.00 (1.58, 10.14)], had a history of atopy [4.3 (1.6, 11.54)], eosinophils >0.2×10⁹/L [3.07 (1.10, 8.61)] and decreased with age [0.97 (0.94, 0.99)]. Finally, in a multivariable model, only male gender and history of atopy remained significant, independent factors, 4.32 (1.61, 11.68) and 4.65 (1.63, 13.26), respectively.

Conclusions: Our research shows that a history of atopy and being male are the strongest, independent predictors for increased FeNO levels in individuals at risk of asthma, while an eosinophil count >0.2×10⁹/L and young age also retain some predictive ability.

Keywords: Asthma; airway inflammation; fractional exhaled nitric oxide (FeNO)