Definition of COPD: based on evidence or opinion?

In 1986, the American Thoracic Society (ATS) first suggested a fixed ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC) ,0.75 to define airflow obstruction [1]. Subsequent ATS documents published in 1991 [2] and 1995 [3] generically defined airflow obstruction as a reduction of FEV1/FVC, without recommending any numerical cut-off point. By contrast, the European Respiratory Society (ERS) guidelines [4] suggested the diagnosis of airflow obstruction be based on a ratio of FEV1 to slow vital capacity (VC) ,88 and ,89% of predicted in males and females, respectively. These values were not arbitrarily chosen as they roughly correspond to the lower 95th percentiles of frequency distributions of a healthy population. More importantly, they are consistent with the well-known decrease of lung elastic recoil and, by inference, of forced expiratory flow with ageing. In 2001, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) took a step back, defining chronic obstructive pulmonary disease (COPD) by a fixed FEV1/FVC ,0.70 [5]. Since then, the enthusiasm for having new guidelines has led the scientific community to overlook the possible consequences of such a definition, even if it was already clear that it may be a source of falsely positive cases in the general population [6]. This was confirmed in a study in the USA [7] evaluating the impact of different definitions of airflow obstruction on the epidemiology of COPD. Quoting CELLI et al. [7], ''differences may be large, altering population prevalence estimates of COPD by .200%''. It is noteworthy that, using FEV1/FVC,0.70, the prevalence of COPD in individuals aged o70 yrs would be o40%.