The Value Of Fractional Exhaled Nitric Oxide In The Diagnosis Of Asthma–COPD Overlap

Objective:To explore the value of fractional exhaled nitric oxide（Fe NO）measurement in the diagnosis of asthma—chronic obstructive pulmonary disease（COPD）overlap.Methods:In this study,we retrospectively analyzed patients suspected with asthma and COPD through physician’s opinion who were admitted to the First hospital of Lanzhou University From June 2015 to June 2017,Finally,a total of 146 patients were enrolled in this study:55 had asthma,39 had COPD,and 52 were diagnosed with ACO.The patient clinical characteristics were collected,such as:gender,age,height,weight.Whether they have allergic rhinitis or not and the smoking history were also collected.All the patients enrolled were subjected to FeNO measurement,pulmonary function test（PFT）,and bronchial hyper responsiveness or bronchodilator test.The correlation between FeNO value and FEV1 improvement rate of bronchial diastolic test and pulmonary function in asthma-COPD overlap group was analyzed.Receiver operating characteristic（ROC）curves were obtained to elucidate the clinical functions of FeNO in diagnosing ACO.Results:（1）The levels of FeNO in ACO group was24.5(38.75ppb(parts per billion,1ppb=1×10^-9),which was significantly higher than COPD group（14.0[10.0]）ppb)and lower than asthma group（51.0[60.0]ppb）.The levels of FeNO in asthma group was significantly higher than COPD group and ACO group.The difference of FeN0 values between asthma group,COPD group and ACO group was statistically significant（P<0.005）.（2）The area under the ROC curve was estimated to be 0.717 for FeNO.Results also revealed an optimal cutoff value of>24.5ppb FeNO for differentiating ACO from COPD patients（sensitivity 50%,specificity 87.2%）.（3）The levels of FeNO in ACO group was pasitively correlated to FEV1 in asthma group,while no correlation was found between Fe NO and FEV1/FVC、PEF、MVV、VC or FEV1in asthma-COPD overlap and COPD group.（4）The levels of Fe NO in ACO group was positively correlated to the improvement rate of FEV1.Conclusion:FeNO measurement is an effective method for distinguishing patients with asthma-COPD overlap from COPD.COPD patients with the level of FeNO higher than 24.5ppb should consider the possibility of asthma-COPD overlap.