Practical Guide to the Identification and Diagnosis of Asthma-COPD Overlap (ACO)

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of mortality around the world. COPD is characterised by a heterogeneous clinical presentation and prognosis which may vary according to the clinical phenotype. One of the phenotypes of COPD most frequently studied is the asthma-COPD overlap (ACO), however, there are no universally accepted diagnostic criteria for ACO. It is recognised that the term ACO includes patients with clinical features of both asthma and COPD, such as more intense eosinophilic bronchial inflammation, more severe respiratory symptoms and more frequent exacerbations, but in contrast, it is associated with a better prognosis compared to COPD. More importantly, ACO patients show better response to inhaled corticosteroid treatment than other COPD phenotypes. The diagnosis of ACO can be difficult in clinical practice, and the identification of these patients can be a challenge for non-specialized physicians. We describe how to recognise and diagnose ACO based on a recently proposed Spanish algorithm and by the analysis of three clinical cases of patients with COPD. The diagnosis of ACO is based on the diagnosis of COPD (chronic airflow obstruction in an adult with significant smoking exposure), in addition to a current diagnosis of asthma and/or signficant eosinophilia.