Asthma

The allergen most frequently associated with asthma is house dust mites.

Asthma Mimics

1. Acid reflux
2. Churg-Strauss syndrome
3. ABPA

In 2024 NICE, the British Thoracic Society and SIGN produced joint guidelines on the management of asthma following many years of conflicting guidelines. The new guidelines represent a major step change in the management of asthma is both diagnosed and treated.

Investigating suspected asthma in adults

First-line investigations NICE

• measure the eosinophil count OR fractional nitric oxide (FeNO)
• diagnose asthma, without further investigations, if:
  • eosinophil is above the reference range
  • FeNO is ≥ 50 ppb

If asthma is not confirmed by the eosinophil count or FeNO

• measure bronchodilator reversibility (BDR) with spirometry
• diagnose asthma if:
  • the FEV1 increase is ≥ 12% and 200 ml or more from the pre-bronchodilator measurement, or
  • the FEV1 increase is ≥ 10% of the predicted normal FEV1
• if spirometry is not available or it is delayed, measure peak expiratory flow (PEF) twice daily for 2 weeks
• diagnose asthma if:
  • PEF variability (expressed as amplitude percentage mean) is ≥ 20%

If asthma is not confirmed by eosinophil count, FeNO, BDR or PEF variability but still suspected on clinical grounds:

• refer for consideration of a bronchial challenge test
• diagnose asthma if bronchial hyper-responsiveness is present