Values of fractionalexhaled nitric oxide in the diagnosis of chronic cough

：Objective To evaluatethe diagnostic value of fractional exhaled nitric oxide(FeNO)in the diagnosis of chroniccough.Methods A total of 106 subjects with chronic cough and normal chest radiographs wererecruited from October 2009 to September 2010.Based on the management guidelines of theChinese Respiratory Society for cough,the golden standard methods were used to make thedefinite diagnosis of chronic cough,including sputum cell counts,pulmonary functiontests,bronchial hyperresponsiveness,24-h esophageal pH monitoring,skin pricking test andserum immunoglobulin E.All subjects received a FeNO test by a NIOXMINO analyzer.The valuesof FleNO to diagnose cough variant asthma(CVA)from chronic cough and EB from non-asthmacough were respectively assessed by the receiver operatingcharacteristic(ROC)curves.Results Among them,the definite diagnoses were cough variantasthma(CVA,n=39),eosinophilic bronchitis(EB,n=30)and other causes(n=37).The FeNO levels inCVA[(54±21)ppb]](1 ppb=1×109mol/L)were significantly higher than those in EB[(34±17)ppb,P<0.01]andother causes[(21±10)ppb,P<0.01].And the FeNO levels in EB were higher than those inother causes(P<0.01).To diagnose CVA from chronic cough,the optimal FeNO cutoff valuewas 40 ppb with a sensitivity of 75%,a specificity of 86%,a positive predictive value of77%,a negative predictive value of 86%and an accuracy of 81%.To diagnose EB fromnon.asthma chronic cough,the optimal FeNO cutoff value was 31 ppb with a sensitivity of63%,a specificity of 92%.a positive predictive value of 88%,a negative predictive value of92%and an accuracy of 72%respectively.Condusion Thereare significant differences betweenthe FeNO levels of different causes of chronic cough.A marked elevation of FeNO levelhelps to make a final diagnosis of CVA or EB.FeNO test is useful for making the diagnosisand differential diagnosis of chronic cough in clinic practices.