Chronic obstructive pulmonary disease diagnosis: the simpler the better? Not always

The acronym chronic obstructive pulmonary disease (COPD) has been introduced in the early 1960s to describe a disease characterized by largely irreversible airflow obstruction, due to a combination of airway disease and pulmonary emphysema, without defining their respective contribution to the pathology. COPD is a disorder that causes considerable morbidity and mortality. Currently, it represents the fourth leading cause of death in the world, and it is expected to increase both in prevalence and in mortality over the next decades. The most widely adopted definition of COPD is that of the Global Initiative for Chronic Obstructive Lung Disease (GOLD), that recommends the use of the post-bronchodilator forced expiratory volume in the first second to forced vital capacity ratio (FEV1/FVC)<0.7 to define irreversible airflow obstruction. This approach, called "fixed ratio", has been introduced to provide a simple tool for COPD diagnosis, as it is easy to remember. Even if modern medicine and research seem to prefer rigid cut-offs and classifications, this often contrasts with the complex nature of the disease. The aim of the present review is to explain that such a fixed cut-off failed to increase COPD diagnosis, and furthermore often leads to inescapable misclassification of patients, with the risk of an excessive simplification of a clinical approach necessarily complex.