Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX
Confirming a diagnosis of asthma in adults requires both a suggestive clinical history and supporting objective tests NICE NG245. The diagnosis should not be confirmed without both elements NICE NG245.
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 NICE NG245. Asthma is diagnosed if the eosinophil count is above the laboratory reference range or the FeNO level is 50 ppb or more NICE NG245.
- Bronchodilator Reversibility (BDR) with Spirometry: If asthma is not confirmed by eosinophil count or FeNO, measure BDR with spirometry NICE NG245. 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 NICE NG245.
- Peak Expiratory Flow (PEF) Variability: If spirometry is unavailable or delayed, measure PEF twice daily for 2 weeks NICE NG245. Asthma is diagnosed if PEF variability (expressed as amplitude percentage mean) is 20% or more NICE NG245.
- 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 NICE NG245. Asthma is diagnosed if bronchial hyper-responsiveness is present NICE NG245.
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) NICE NG245. It also includes identifying triggers, a personal or family history of asthma or allergic rhinitis, and symptoms suggesting alternative diagnoses NICE NG245.