Table 1.
Usual features of asthma, COPD, and ACOS
| Feature | Asthma | COPD | ACOS |
|---|---|---|---|
| Age of onset | Usually childhood onset but can commerce at any age | Usually >40 years of age | Usually >40 years of age, but may have had symptoms in childhood or early adulthood |
| Pattern of respiratory symptoms | Symptoms may vary over time (day to day, or over longer periods), often limiting activity. Often triggered by exercise, emotions, dust, or exposure to allergens | Chronic usually continuous symptoms, particularly during exercise, with “better” and “worse” days | Respiratory symptoms including exertional dyspnea are persistent but variability may be prominent |
| Lung function | Current and/or historical variable airflow limitation, for example, BD reversibility, AHR | FEV1 may be improved by therapy, but post‐BD FEV1/FVC <0.7 persists | Airflow limitation not fully reversible, but often with current or historical variability |
| Lung function between symptoms | May be normal between symptoms | Persistent airflow limitation | Persistent airflow limitation |
| Past history or family history | Many patients have allergens and a personal history of asthma in childhood, and/or family history of asthma | History of exposure to noxious particles and gases (mainly tobacco smoking and biomass fuels) | Frequently a history of doctor‐diagnosed asthma (current or previous), allergens and a family history of asthma, and/or a history of noxious exposures |
| Time course | Often improves spontaneously or with treatment, but may result in fixed airflow limitation | Generally, slowly progressive over years despite treatment | Symptoms are partly but significantly reduced by treatment. Progression is usual, and treatment needs are high |
| Chest X‐ray | Usually normal | Severe hyperinflation and other changes of COPD | Similar to COPD |
| Exacerbations | Exacerbations occur, but the risk of exacerbations can be considerably reduced by treatment | Exacerbations can be reduced by treatment. If present, comorbidities contribute to impairment | Exacerbations may be more common than in COPD but are reduced by treatment. Comorbidities can contribute to impairment |
| Airway inflammation | Eosinophils and/or neutrophils | Neutrophils and/or eosinophils in sputum, lymphocytes in airways, may have systemic inflammation | Eosinophils and/or neutrophils in sputum |
ACOS, asthma COPD overlap syndrome; BD, bronchodilator; AHR, airway hyper‐responsiveness; COPD, chronic obstructive pulmonary disease.