What are the key diagnostic criteria for asthma in adults presenting w

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Key diagnostic criteria for asthma in adults presenting with respiratory symptoms include:

A suggestive clinical history of asthma symptoms such as wheeze, noisy breathing, cough, breathlessness, or chest tightness, with variation in symptoms (e.g., worse at night or early morning, or seasonal) and any known triggers, plus a personal or family history of asthma or allergic rhinitis. Alternative diagnoses should be considered and excluded .
Objective confirmation is required before diagnosis; code as suspected asthma until confirmed .
Objective tests include:

Blood eosinophil count or fractional exhaled nitric oxide (FeNO) measurement: asthma is diagnosed if eosinophil count is above the laboratory reference range or FeNO is ≥50 ppb .
If eosinophil count or FeNO is not diagnostic, perform spirometry with bronchodilator reversibility (BDR) testing: an increase in FEV1 of ≥12% and ≥200 ml from baseline (or ≥10% of predicted FEV1) confirms asthma .
If spirometry is unavailable or delayed, measure peak expiratory flow (PEF) twice daily for 2 weeks; a variability of ≥20% supports diagnosis .
If still unconfirmed but clinical suspicion remains, refer for bronchial challenge testing to detect bronchial hyper-responsiveness .

Physical examination may reveal expiratory polyphonic wheeze but can be normal even in asthma .

What are the key diagnostic criteria for asthma in adults presenting with respiratory symptoms?