[The diagnostic value of the fractional exhaled nitric oxide for cough variant asthma in children].

Objective: To determine the diagnostic value of fractional exhaled nitric oxide (FeNO) measurement in diagnosis of Cough Variant Asthma (CVA) in children.

Methods: Outpatients with a cough > 4 weeks visiting The Children's Hospital Affiliated to Suzhou University from March 2012 to April 2013 were enrolled. FeNO was measured by a nitric oxide analyzer in accordance with American Thoracic Society guidelines. The levels of FeNO in CVA and other causes of chronic cough were compared. The value of FeNO was assessed and the optimal operating point of FeNO testing for the diagnosis of CVA was determined by the means of the receiver operating characteristic (ROC) curves.

Results: A total of 84 children with chronic cough were recruited, among whom 38 were diagnosed as having CVA. The levels of FeNO were not statistically different between patients with CVA [(37.2 ± 13.8) ppb] and patients with CVA combined with upper airway cough syndrome [UACS, (40.1 ± 13.8) ppb, P = 0.124], but were both significantly higher than those in patients with UACS or with postinfectious cough (PIC), and the normal control group (P < 0.01 respectively). There were 46 non-CVA patients, including 34 cases with UACS and 12 PIC, and their FeNO levels were not statistically different [(18.3 ± 7.6) to (19.2 ± 4.4) ppb, t = 2.580, P = 2.996]. The levels of FeNO declined rapidly in CVA patients after inhaled corticosteroids during the 4 week follow-up. The proportion of eosinophils in the sputum from CVA patients was higher than that from the non-CVA patients, consistent with the level of FeNO, which showed a positive linear correlation with sputum eosinophils. The area under ROC curve was 0.94.The optimal diagnostic cutoff point was 22.5 ppb which was capable of differentiating CVA and non-CVA with a sensitivity of 84%, and a specificity of 94.3%.

Conclusions: The level of FENO was higher in CVA compared to other causes of chronic cough. FeNO, a marker of airway eosinophilic inflammation, may be helpful in the diagnosis of CVA in children with high sensitivity and specificity.