Towards precision in defining COPD exacerbations

COPD is the most prevalent chronic respiratory disease worldwide and a major cause of disability and death. Acute exacerbations of COPD remain a key feature of the disease in many patients and research assessing interventions to prevent and treat them requires a robust definition with high sensitivity and specificity. To date, no such definition exists, and multiple different definitions are used in clinical studies depending on the research question. The strengths and weaknesses of current definitions are discussed in the context of evolving knowledge and different settings in which studies are undertaken. Whether identification and recording of exacerbations remains essentially clinical, or can be identified with a dependable biomarker, it should be sensitive and adaptable to context while retaining clarity and facilitating data collection. This is essential to progress a better understanding of the pathophysiology and phenotypic expression of exacerbations to reduce their impact and personal burden for patients.