ABSTRACT
<p><b>OBJECTIVE</b>To evaluate fractional exhaled nitric oxide (FENO) level in patients with subacute cough and its value in predicting the patients' response to inhaled corticosteroids (ICS) treatment.</p><p><b>METHODS</b>A total of 100 patients with persistent cough lasting more than 3 weeks were enrolled, including 52 patients with subacute cough and 48 with chronic cough. FENO, spirometry, and responses to ICS therapy of the patients were evaluated.</p><p><b>RESULTS</b>The recruited patients had a median (inter-quartile ranges) FENO level of 19 ppb (12-30 ppb). Patients with chronic cough had a significantly higher median FENO level than those with subacute cough (20.5 vs 16 ppb; Z=-2.245, P=0.025). A FENO level ≥25 ppb was recorded in 15 (28.8%) patients with subacute cough, as compared with 20 (41.6%) in patients with chronic cough (χ(2)=1.801, P=0.179). With a FENO ≥25 ppb as the critical value to justify ICS treatment, 15 patients with subacute cough received ICS and 14 (93.3%) of them showed obvious relief of cough after 2 weeks of therapy, a response rate similar to that of 85.0% (17/20) in patients with chronic cough receiving the treatment (χ(2)=0.588, P=0.443). In patients with subacute cough, those with cough variant asthma (CVA) or eosinophilic bronchitis (EB) had a significantly higher median FENO level than those with postinfectious cough [(16 (11-31) ppb vs 11 (8-19) ppb, P<0.01]. In the etiological analysis, CVA or EB was identified in 23 (44.2%) of the patients with subacute cough, as compared 21 (43.8%) in patients with chronic cough (χ(2)=0.002, P=0.961).</p><p><b>CONCLUSION</b>FENO may be an important indicator for etiological diagnosis of subacute cough and for predicting the response to ICS treatment.</p>