Association between fractional exhaled nitric oxide (FeNO) cutoff values (25 ppb) and risk factors of cough.

IntroductionCough is among the most common symptoms for patients to seek medical attention. ObjectivesThe purpose of this study is to evaluate the association between fractional exhaled nitric oxide (FeNO) cutoff values (25 ppb) and risk factors related to cough, hoping to evaluate the feasibility of the FeNO cut point values (25 ppb) for clinical prediction of cough in etiology. MethodsIn 107 adult patients with acute, subacute, or chronic cough, the FeNO, forced expiratory volume for 1 second (FEV1), forced vital capacity (FVC), blood routine (white blood cell and neutrophil), immunoglobulin E (IgE), lymphocyte eosinophils, and hemoglobin were measured. The Student's t-test was used to test the differences of FeNO levels compared with FEV1/FVC, lymphocyte, and hemoglobin level. For evaluating the correlation of FeNO levels with IgE, eosinophil, blood routine, pulmonary infection, and smoking status, the chi-square test was performed. ResultsFeNO cutoff value (25 ppb) significantly correlated with serum IgE (P<.0001) between 200 IU/mL and <200 IU/mL level, eosinophil (P=.039) between 5% and <5% level, lymphocyte percentage (P=.032) and the ratio of FEV1/FVC (P=.032), while weakly correlated with pulmonary infection, blood routine (white blood cell and neutrophil), hemoglobin, and smoking. ConclusionThe cutoff values of FeNO (25 ppb or <25 ppb) are useful for etiological detection of cough with high sensitivity.