To determine the impact of changing reference standards (RS), namely spirometry versus whole body plethysmography (WBP), on estimation of the diagnostic accuracy of Fractioned exhaled Nitric Oxide (FeNO) and clinical signs and symptoms (CSS) as index tests regarding asthma diagnosis.
Diagnostic study in 393 patients attending a private practice of pneumologists with complaints suspicious of asthma. Firstly, the index tests were compared to the diagnostic results of spirometry in terms of FEV responsiveness. Secondly, the index tests were compared to the results of WBP in terms of specific airway resistance and FEV responsiveness. Areas under the curve (AUC) were compared with a generalized estimating equation approach based on binary logistic regression.
FeNO values and CSS ´wheezing´ and ´allergic rhinitis´ showed higher specificities (p<0.001) and sensitivities (not significant) when evaluated with WBP; also Youden-indices increased in these CSS (p<0.05). AUC of FeNO in combination with ´wheezing´ and ´allergic rhinitis´ when WBP was used as RS (AUC=0.724; 95%CI 0.672 to 0.776) was higher compared to spirometry as RS (AUC=0.654; 95%CI 0.585 to 0.722) (p<0.001).
In case of asthma, superior RS led to more favorable assessment of index tests. FeNO measurement might have been underestimated in some previous studies.

Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.