FeNO for detecting lower airway involvement in patients with allergic rhinitis

Allergic rhinitis (AR) is a risk factor for asthma development. The value of fractional exhaled nitric oxide (FeNO) in detecting lower airway involvement in the progress of AR-asthma march has not been evaluated. The aim of the present study was to investigate the value of FeNO in assessing lower airway inflammation and predicting bronchial hyperresponsiveness (BHR) in AR with or without asthma. FeNO and eosinophil count in induced sputum, and a methacholine bronchial provocation test were performed in 93 subjects, including: 45 AR patients (AR group); 20 patients with AR and asthma (AR with asthma group); and 28 normal controls (control group). The AR group was divided into two sub-groups: AR with asymptomatic BHR group and AR without BHR group. Correlation between FeNO and eosinophil count was assessed. Receiver operating characteristic (ROC) curve was applied to evaluate the predictive and diagnostic value of FeNO in detecting BHR. The values of FeNO in the AR and AR with asthma groups were higher [29.5 (22.0) ppb and 61.5 (33.0) ppb] compared with the normal control group (16.0 (10.0) ppb), where the values in brackets indicate the interquartile range of the values. The percentages of eosinophils in induced sputum were 2.43±3.56, 7.36±4.98 and 18.58±11.26% in the control, AR and AR with asthma groups, respectively. For the diagnosis of BHR, the area under the curve (AUC) was 0.910 (95%CI 0.836, 0.984), with the sensitivity and specificity 0.846 and 0.817 when the cut-off value takes 31.5 ppb. For diagnosis of asthma, the AUC was 0.873 (95%CI 0.753, 0.992) with sensitivity 0.857 and specificity 0.847 when taking the cut-off value to be 38.0 ppb. The value of FeNO was well correlated with eosinophil count in the sputum. The measurement of FeNO is an effective method in detecting lower airway involvement in AR developing to asthma.