• N Fens, A C Roldaan, M P van der Schee, R J Boksem, A H Zwinderman, E H Bel, and P J Sterk.
• Department of Respiratory Medicine, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands. N.Fens@amc.nl
• Clin. Exp. Allergy. 2011 Oct 1;41(10):1371-8.

BackgroundFixed airflow limitation can be found both in asthma and chronic obstructive pulmonary disease (COPD), posing a day-to-day diagnostic challenge.ObjectiveWe aimed to determine the external validity of metabolomic analysis of exhaled air by electronic nose for distinguishing asthma and COPD in patients with fixed airways obstruction.MethodsOne hundred patients were included in a cross-sectional design: 60 asthma patients: 21 with fixed airways obstruction (fixed asthma), 39 with reversible airways obstruction (classic asthma) and 40 COPD patients (GOLD stages II-III). Standardized sampling of exhaled breath was performed and volatile organic compounds were captured using an electronic nose resulting in breathprints. External validity in newly recruited patients (validation sets) was tested using a previous and independent training set. Breathprints were analysed by principal component and canonical discriminant analysis and area under the curve (AUC) of receiver operating characteristic curves.ResultsExternal validity of breathprints showed 88% accuracy for distinguishing fixed asthma from COPD (AUC 0.95, 95% CI 0.84-1.00, sensitivity 85%, specificity 90%) and 83% for classic asthma (AUC 0.93, 95% CI 0.87-1.00, sensitivity 91%, specificity 90%) (both P<0.001). Discriminative accuracy was not confounded by current smoking.Conclusions And Clinical RelevanceExternal validation of exhaled breath molecular profiling shows high accuracy in distinguishing asthma and COPD in newly recruited patients with fixed airways obstruction. Exhaled air analysis may therefore reduce misdiagnosis in obstructive airways diseases, potentially leading to more appropriate management.© 2011 Blackwell Publishing Ltd.

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