Determination of a Cut-off Point for Exhaled Nitric Oxide in the Diagnosis of Asthma in an Iranian Population

Asthma is a major source of global social and economic burden; thus, its early detection is important. Measurement of fractional exhaled nitric oxide (FENO) has been used recently considered a good indicator of asthma and also a sensitive and non-invasive method for monitoring airway inflammation. This study was conducted to determine the cut-off point of FENO for the diagnosis of asthma in the studied population.
The subjects of this cross-sectional diagnostic study were assessed by the FENO test, spirometry, and methacholine challenge test. The best cut-off point of the FENO for the diagnosis of asthma was determined. The data were analyzed by SPSS 20 using student t-test, and Chi-square test and the ROC curves were also drawn.
The mean FENO in asthmatic and non-asthmatic subjects was 43.5±33.41 and 17.5±21.48 ppb, respectively (P <0.001). The best cut-off point of the FENO based on the overall sensitivity and specificity was 39.5 ppb.
According to the results of this study, symptomatic patients with FENO higher than 39.5 ppb could be considered as asthmatic.