Diagnostic value of fractional exhaled nitric oxide for cough variant asthma

Abstract:

Objective：To explore the clinical value and possible influencing factors of fractional exhaled nitric oxide（FeNO） in patients with cough variant asthma（CVA）. Methods：Totally 607 patients with chronic cough consecutively referred to our hospital from October 2015 to September 2016 were selected. All cases were carried out FeNO measurement at first；next，spirometry，bronchoprovocation tests or bronchodilation tests and combining with the history were used to confirm or exclude CVA. Logistic regression model was established to analyze the factors associated with CVA. Receiver operating characteristic curve（ROC） was used to determine the best cut-off value of FeNO for CVA diagnosis and to evaluate the diagnostic value of FeNO and FeNO combined with other related factors in CVA. Results：Totally 331 cases were diagnosed as CVA and the other 276 cases were non-CVA. FeNO levels of CVA group were significantly higher than those of non-CVA group[（54.7±44.5） ppb vs. （19.8±11.9） ppb，P<0.01]. 31 ppb was the best cut-off value of FeNO identifying CVA with the sensitivity of 61.63% and the specificity of 89.13%. The area under ROC curve was 0.794. The maximum value of Youden’s index was 0.507 6. The positive predictive value was 87.18%，the negative predictive value was 65.95%. The increase of age caused the decrease of FeNO. The area under the ROC curve of FeNO combined with age and smoking history for diagnosing CVA was 0.813，which was slightly higher than the area under the ROC curve under the single use of FeNO，but the dif－ference between them was not statistically significant（P=0.224）. Conclusion：FeNO test is an effective auxiliary diagnosis method for CVA，which is helpful for the differential diagnosis of chronic cough. The diagnostic value of FeNO combined with other related factors for patients with CVA is not better than that of FeNO alone.