C4.1 Confirm or exclude asthma

If airflow limitation is fully or substantially reversible, (FEV1 response to bronchodilator>400ml), the patient should be treated as for asthma (British Thoracic Society 2008a, Hunter 2002)

Asthma and COPD are usually easy to differentiate. Asthma usually runs a more variable course and dates back to a younger age. Atopy is more common and the smoking history is often relatively light (eg, less than 15 pack-years). Airflow limitation in asthma is substantially, if not com­pletely, reversible, either spontaneously or in response to treatment. By contrast, COPD tends to be progressive, with a late onset of symptoms and a moderately heavy smoking history (usually >15 pack-years) and the airflow obstruction is not completely reversible.

However, there are some patients in whom it is difficult to distinguish between asthma and COPD as the primary cause of their chronic airflow limitation. Long-standing or poorly controlled asthma can lead to chronic, irreversible airway narrowing even in non-smokers, thought to be due to airway remodelling resulting from uncontrolled airway wall inflammation with release of cytokines and mediators.

Furthermore, asthma and COPD are both common conditions, and it must be expected that the two can coexist as least as often as the background prevalence of asthma in adults.