ABSTRACT
An exacerbation of chronic obstructive pulmonary disease (COPD) may appear in a wide range of presentations from increased symptoms to hospitalizations, respiratory failure, and death (1). Accordingly, the definition of exacerbations both for clinical purposes and in research has been controversial (2). Because identification of exacerbations may be difficult and costly, many epidemiological studies have used hospital admissions due to COPD exacerbations as a surrogate of exacerbation.
