Utility of fractional exhaled nitric oxide (FENO) measurements in diagnosing asthma

Background: To facilitate the use of fractional exhaled nitric oxide (FENO) as a clinical test, FENO measurements need more clarification. Aim: We sought to evaluate the yield of FENO measurement for the diagnosis of asthma and identify the determinants of FENO in children. Methods: Two hundred forty five consecutive steroid-naive patients aged 8-16 years with symptoms suggestive of asthma were included. Children were evaluated using FENO measurements, questionnaires, skin prick tests, spirometries, and methacholine challenge tests. Results: Asthma was diagnosed in 167 children. The sensitivity, specificity, and positive (PPV) and negative predictive values (NPV) of FENO measurements for the diagnosis of asthma at the best cutoff value of 22 ppb were 56.9%, 87.2%, 90.5%, and 48.6%, respectively. At a cutoff value of 42 ppb, specificity and PPV were all 100% but at the cost of very low sensitivity (23.4%) and NPV (37.9%). Both atopy and asthma were identified as independent risk factors associated with high FENO. The association of asthma with high FENO was found only in atopic children because FENO was low in non-atopic children regardless of asthma status. Although highest FENO was observed in atopic asthmatic patients, 28% of these patients had FENO values lower than 22 ppb. Conclusion: Atopic asthmatic patients with low FENO values and non-atopic asthmatic patients were responsible for false-negative cases that might contribute to low sensitivity of FENO measurements in diagnosing asthma. High specificity of FENO measurements may help identify patients with atopic asthma among subjects with respiratory symptoms. (C) 2012 Elsevier Ltd. All rights reserved.