RESULTS: A total of 302 patients with chronic cough (CVA, n=95; EB, n=63; UACS, n=24; GERC, n=26 and other causes, n=94) and 163 patients with classic asthma were included in this study. Median FeNO concentration in CC, CA, CA+CVA with sputum eosinophilia was significantly higher than that in CC, CA, CA+CVA without sputum eosinophilia [37.5 (21.0-72.8) ppb vs 16.0 (10.0-22.0) ppb; 55.0 (32.0-92.0) ppb vs 22.0 (15.3-31.5) ppb; 56.0 (34.0-92.0) ppb vs 19.5 (13.3-31.5) ppb, p<0.01 respectively]. Significant positive correlations existed between FeNO and sputum eosiniphils in CC (rs =0.574, p<0.01), CA (rs =0.419, p<0.01), CVA+CA (rs =0.414, p<0.01), respectively. The optimal cut off level of FeNO was 29.5 ppb with sensitivity of 62.0% and specificity of 88.2% for predicting sputum eosinophilia from non-sputum eosinophilia in CC. With the cutoff point of 34.5 ppb, the sensitivity and specificity for differentiating CA with sputum eosinophilia from without sputum eosinophilia were 74.1% and 83.3%. FeNO of 34.5 ppb had a sensitivity and specificity of 74.3% and 79.5% in predicting sputum eosinophilia in asthma (CA+CVA).