Blood eosinophil count: a biomarker of an important treatable trait in patients with airway disease

Inhaled corticosteroids (ICS) are widely used to treat patients with chronic obstructive pulmonary disease (COPD). Their main impact is to reduce the risk of exacerbations; in contrast to long-acting bronchodilators their effects on symptoms and lung function are small and insufficient to use as a guide of treatment efficacy. As a result, ICS are applied in a “risk-directed” fashion, with treatment directed at patients deemed to be at risk of exacerbations because of a past history of events, and/or poor lung function 1. A better, more precise strategy would be to apply treatment in a targeted fashion according to a biomarker indicating the likelihood that corticosteroid treatment will have a positive effect on the outcome of interest ( i.e. reduction in exacerbations or decline in lung function). Blood eosinophil count can identify eosinophilic airway inflammation, a “treatable trait” of COPD