Asthma and COPD are considered as chronic airway inflammatory diseases, which are typically associated with Th2-mediated immune response in asthma and related to the characteristics of Th1-mediated immunity in COPD . Asthma-COPD overlap (ACO) is the term to describe patients who have features of both asthma and COPD, recom¬mended by the 2019 Global Initiative for Asthma (GINA) and the Global Initiative for Chronic Obstruction Lung Disease (GOLD) guidelines. Patients with asthma and COPD are commonly seen in clinical practice. In addition, compared with patients with asthma or COPD alone, patients with ACO experience frequent exacerbations and hospitalizations, have poor quality of life, a more rapid decline in lung function and high mortality, and consume a disproportionate amount of health care resources than asthma or COPD alone .
Cell count in induced sputum is a noninvasive biomarker to assess airway inflammation phenotypes. Accordingly, sputum cell counts are extensively used in the treatment of asthma and COPD. Nevertheless, the clinical application of sputum cell counts in patients with asthma-COPD overlap (ACO) remains elusive .
