Exhaled nitric oxide as a noninvasive assessment of chronic cough

Exhaled nitric oxide (ENO) has been suggested as a marker of airway inflamm ation. This study aimed to evaluate the role of ENO in the investigation of chronic cough. We measured ENO in 38 adult patients reporting chronic coug h, in 23 healthy control subjects, and in 44 asthmatics. In addition to the regular investigation, ENO was measured by a chemiluminescent analyzer usi ng the restricted breath technique. In the chronic cough group, 30 were con sidered as nonasthmatic, whereas asthma was diagnosed in eight by a positiv e methacholine challenge. ENO values were significantly higher in patients with chronic cough attributable to asthma as compared with those with chron ic cough not attributable to asthma and to healthy volunteers (75.0 ppb; 16 .7 ppb; and 28.3 ppb, respectively). The sensitivity and specificity of ENO for detecting asthma, using 30 ppb as the ENO cutoff point, were 75 and 87 %, respectively. The positive and negative predictive values were 60 and 93 %, and the positive and negative likelihood ratios were 5.8 and 0.3, respec tively. We conclude that ENO may have a role in the evaluation of chronic c ough. In this group of patients, low ENO suggested little likelihood of ast hma. The patients with chronic cough not attributable to asthma showed a lo w ENO value as compared with healthy volunteers and asthmatics.