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.

Conclusions: 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.