Diagnostic Approach to Asthma in Adults

Initial Diagnostic Evaluation

The American Academy of Allergy, Asthma, and Immunology recommends spirometry as the essential first-line objective measure to establish an asthma diagnosis in adults, as medical history and physical examination cannot reliably exclude other diagnoses or assess lung status 1, 2
Objective tests should be performed to confirm asthma before initiating long-term therapy, even when symptoms are highly suggestive, according to the British Thoracic Society 3, 4
The diagnosis of asthma requires demonstrating reversible airflow obstruction: an increase in FEV₁ of ≥200 mL AND ≥12% from baseline after inhaling a short-acting β₂-agonist, as recommended by the American College of Chest Physicians 1, 2

Spirometry is indicated when a patient presents with variable, intermittent symptoms including wheeze, shortness of breath, chest tightness, or cough, according to the European Respiratory Society 3, 4
Symptoms worse at night or provoked by triggers (exercise, viral infections, allergens, irritants) also suggest asthma, as stated by the American Thoracic Society 3, 1
Personal or family history of asthma or atopic conditions is also a relevant factor, as noted by the British Thoracic Society 3, 4

The European Respiratory Society explicitly recommends against using empiric treatment trials where symptom improvement alone confirms diagnosis, as this approach leads to misdiagnosis 5, 6

Peak expiratory flow (PEF) variability monitoring: ≥20% diurnal variation (amplitude % best method) with minimum change of 60 L/min over 2 weeks is highly suggestive of asthma, according to the British Thoracic Society 3, 4
Measure fractional exhaled nitric oxide (FeNO): a value ≥25 ppb supports asthma diagnosis, as recommended by the European Respiratory Society 5, 6

At age 35, objective testing is particularly important to differentiate asthma from chronic obstructive pulmonary disease (COPD) in smokers, vocal cord dysfunction, cardiac causes (congestive heart failure, pulmonary embolism), and mechanical airway obstruction (tumors), as stated by the American College of Chest Physicians 1, 2

Spirometry should be repeated at least every 1-2 years once asthma is diagnosed and treatment initiated, according to the American Academy of Family Physicians 7