Barczyk A, et al. - Five different asthma-chronic obstructive pulmonary disease overlap (ACO) definitions, including the GINA/GOLD criteria, were examined for their concordance. Further, researchers determined the definition-based ACO prevalence and characteristics. The final analysis included 1609 patients. Thirty-one ACO subpopulations were identified with the application of Venn diagram for ACO populations, further reduction to 6 separate populations was noted when a rank order was introduced for the analyzed definitions to classify patients from intersecting groups. Overall, they noted poor level of agreement between different ACO definitions. The current ACO definitions identified distinct populations. Only a small number of common features were shared and different disease phenotypes were present in these populations. ACO prevalence is highly variable, depending on the definition applied. Definition-based ACO prevalence ranged from 3.8% (Spanish criteria) to 18.4% (clinician’s diagnosis).