Validity of Fractional Exhaled Nitric Oxide in Diagnosis of Corticosteroid-Responsive Cough

Background Whether fractional exhaled nitric oxide (FeNO) measurement alone or combined with sputum eosinophil and atopy is useful in predicting corticosteroid-responsive cough (CRC) and non-CRC (NCRC) is not clear. Methods A total of 244 patients with chronic cough and 59 healthy subjects as control were enrolled. The causes of chronic cough were confirmed according to a well-established diagnostic algorithm. FeNO measurement and induced sputum for differential cell were performed in all subjects. Results CRC occurred in 139 (57.0%) patients and NCRC occurred in 105. The FeNO level in CRC significantly correlated with sputum eosinophils (r s  = 0.583, P P Conclusions In our cohort, a high level (≥ 31.5 ppb) of FeNO indicates more likelihood of CRC, but the sensitivity is insufficient to rule out a diagnosis of CRC. A combination of low-level FeNO, normal sputum eosinophil, and absence of atopy suggests a lower likelihood of CRC.