What are the key diagnostic criteria for confirming a diagnosis of asthma in adults?

Confirming a diagnosis of asthma in adults requires both a suggestive clinical history and supporting objective tests ¹. The diagnosis should not be confirmed without both elements ¹.

Key diagnostic criteria based on objective tests for adults with a history suggestive of asthma:

• Blood Eosinophil Count or Fractional Exhaled Nitric Oxide (FeNO): Measure the blood eosinophil count or FeNO level ¹. Asthma is diagnosed if the eosinophil count is above the laboratory reference range or the FeNO level is 50 ppb or more ¹.
• Bronchodilator Reversibility (BDR) with Spirometry: If asthma is not confirmed by eosinophil count or FeNO, measure BDR with spirometry ¹. Asthma is diagnosed if the FEV1 increase is 12% or more and 200 ml or more from the pre-bronchodilator measurement, or if the FEV1 increase is 10% or more of the predicted normal FEV1 ¹.
• Peak Expiratory Flow (PEF) Variability: If spirometry is unavailable or delayed, measure PEF twice daily for 2 weeks ¹. Asthma is diagnosed if PEF variability (expressed as amplitude percentage mean) is 20% or more ¹.
• Bronchial Challenge Test: If asthma is still suspected on clinical grounds but not confirmed by eosinophil count, FeNO, BDR, or PEF variability, refer for consideration of a bronchial challenge test ¹. Asthma is diagnosed if bronchial hyper-responsiveness is present ¹.

Clinical History: A structured clinical history is essential, checking for reported wheeze, noisy breathing, cough, breathlessness, or chest tightness, and any variation (e.g., worse at night or early morning, or seasonal) ¹. It also includes identifying triggers, a personal or family history of asthma or allergic rhinitis, and symptoms suggesting alternative diagnoses ¹.