Inhaled corticosteroids, used for preventing acute exacerbation of chronic obstructive pulmonary disease (COPD), often lead to increased high blood eosinophil count, while low blood eosinophil count is often associated with pneumonia risk—however, the prognostic role of blood eosinophil count has not yet been explored. In a recent study, researchers found that the severity of emphysema was independently linked with low blood eosinophil count and the longer survival period was associated with increased blood eosinophil count.