Variable airflow obstruction, demonstrated objectively
Expansion
The clinical picture: episodic wheeze, cough, chest tightness and breathlessness, worse at night and in the early morning, with recognisable triggers (exercise, cold air, allergens, NSAIDs, beta blockers), a personal or family history of atopy, and diurnal variation.
Objective tests, at least one of which should be positive:
- FeNO 40 ppb or more in adults, 35 in children
- Bronchodilator reversibility: improvement in FEV1 of 12 per cent and 200 ml
- Peak flow variability over 20 per cent on twice daily readings for 2 to 4 weeks
- Obstructive spirometry, with FEV1/FVC below 0.7
- Bronchial challenge testing, in specialist practice
“Asthma is variable; COPD is fixed.” That single contrast is what all these tests are trying to demonstrate.
Occupational asthma accounts for around 1 in 10 adult onset cases and is missed unless asked about: symptoms improve on rest days and on holiday. Confirm with serial peak flow at and away from work over at least two weeks, and refer, because early removal from exposure determines the outcome.
A normal examination and normal spirometry between attacks are expected, and are not evidence against the diagnosis.