Diagnostic value and influencing factors of fractional exhaled nitric oxide in suspected asthma patients.

OBJECTIVE To explore the critical value and possible influencing factors of fractional exhaled nitric oxide (FeNO) in suspected asthma patients. METHODS 923 suspected asthmatics consecutively referred to our hospital during December 2012 to July 2014 were selected. All cases were carried out FeNO measurement at first; next, spirometry, bronchoprovocation tests or bronchodilation tests were used to confirm or exclude asthma. Receiver operating characteristic curve (ROC) was used to determine the best cut-off value of FeNO for asthma diagnosis. RESULTS In bronchoprovocation test, 125 cases were diagnosed as asthma, other 283 were non-asthmatics. FeNO levels of asthmatics were significantly higher than non-asthmatics (median, 64.8 ppb vs. 27.9 ppb, P<0.01). In this group of patients, 64 ppb was the best cut-off value of FeNO to identify asthma with sensitivity of 52.0% and specificity of 94.35%. In bronchodilation test, 185 patients were diagnosed as asthma, other 330 were non-asthmatics. FeNO levels of asthmatics were significantly higher than non-asthmatics (median, 60.6 ppb vs. 29.05 ppb, P<0.01). In bronchodilation test patients, 41 ppb was the best cut-off value of FeNO to identify asthma with sensitivity of 72.43% and specificity of 74.85%. Influencing factors analysis showed that sex was an independent factor affecting patients' FeNO level. CONCLUSION FeNO was an effective auxiliary diagnosis method for bronchial asthma. 64 ppb and 41 ppb was the best cut-off value of FeNO to identify asthma in bronchoprovocation test or bronchodilation test, respectively. Sex was an independent factor affecting patients' FeNO level.