Asthma and chronic obstructive disease overlap (ACO), a systematic review of prevalence and co-morbidity factors based on diagnostic criteria

Background: Asthma and chronic obstructive pulmonary disease (COPD) overlap (ACO) is a complex pathological condition involving features of both asthma and COPD. While the individual diagnoses of asthma and COPD are well defined, there is no consensus on the definition or diagnostic criteria for ACO. This lack of standardisation contributes to inconsistencies in data interpretation and reported prevalence. In this study, we aimed to systematically review the differences in diagnostic criteria and prevalence of ACO across studies, to identify the co-morbidities, and provide insights into the clinical factors associated with ACO. Methods: A systematic review was conducted in accordance with the PRISMA guidelines. A total of 1,033 articles were identified from three electronic databases, of which 37 studies met the inclusion criteria and were included in the final analysis. Results: The reported prevalence of ACO varied widely depending on the study population and diagnostic criteria used. ACO prevalence ranged from 0.55% to 12.9% in the general population, 11.8% to 53.3% among asthma cohorts, 10.5% to 56.2% among COPD cohorts, 4.3% to 47.8% among combined asthma and COPD cohorts, and 3.2% to 18.4% among other respiratory or chronic airway disease cohorts. ACO was commonly associated with co-morbidities such as cardiovascular disease, gastroesophageal reflux disease, diabetes, and allergic rhinitis. Clinical factors linked to ACO included higher body mass index, smoking history, and reduced lung function (FEV1%). Conclusion: The wide variability in ACO prevalence reflects differences in diagnostic definitions and study populations. Patients with ACO experience increased morbidity, including higher rates of exacerbations, hospitalisations, and poorer quality of life, likely due to the presence of multiple co-morbidities. Standardised diagnostic criteria are essential to improve disease recognition and management.