Exhaled nitric oxide in the diagnosis of asthma in adults: a systematic review

SummaryObjectivesTo identify and synthesize evidence on the diagnostic accuracy of FENO for asthma in adults.Materials and MethodsSystematic searches (nine key biomedical databases and trial registers) were carried out on November 2014. Records were included if they recruited patients with the symptoms of asthma; used a single set of inclusion criteria; measured FENO50 in accordance with American Thoracic Society guidelines, 2005 (off‐line excluded); reported/allowed calculation of true‐positive, true‐negative, false‐positive and false‐negative patients as classified against any reference standard. Study quality was assessed using QUADAS II. Meta‐analysis was planned where clinical study heterogeneity allowed. Rule‐in and rule‐out uses of FENO were considered.ResultsA total of 4861 records were identified originally and 1312 in an update. Twenty‐seven studies were included. Heterogeneity precluded meta‐analysis. Results varied even within subgroups of studies. Cut‐off values for the best sum of sensitivity and specificity varied from 12 to 55 p.p.b., but did not produce high accuracy. 100% sensitivity or 100% specificity was reported by some studies indicating potential use as a rule‐in or rule‐out strategy.Conclusions and Clinical RelevanceFENO50 had variable diagnostic accuracy even within subgroups of studies with similar characteristics. Diagnostic accuracy, optimal cut‐off values and best position for FENO50 within a pathway remain poorly evidenced.