OPINION

I have taken my umbrella, so of course it does not rain D S Postma,1,2 G Brusselle,3 A Bush,4 J W Holloway5 Spirometry is used worldwide to diagnose respiratory disease, and it is a validated measure to assess airway obstruction. Irreversible airway obstruction is the defining feature of chronic obstructive pulmonary disease (COPD). Thus, an FEV1/FVC ratio <70 % is used to diagnose COPD, and the severity is thereafter based on the level of FEV1. This definition is widely used in clinical practice and research, yet may lead to confusion with respect to the diagnosis associated with the presence of airway obstruction. The three main reasons are the following: (1) fixed airflow obstruction may be the result of specific diagnoses such a