Asthma — Diagnosis (Adults & Adolescents)

See Asthma — Management for treatment, and Asthma — Children for the under-12 diagnostic approach.

Definition

Asthma is a chronic inflammatory lung condition defined clinically by the combination of:

• Variable respiratory symptoms — wheeze, breathlessness, chest tightness, cough — that vary over time in frequency and severity, AND
• Variable airflow limitation, demonstrated on spirometry, and/or evidence of airway inflammation on fractional exhaled nitric oxide (FeNO) testing.

Asthma affects roughly 1 in 9 Australians. It causes an estimated 55,000 ED presentations and 25,500 hospitalisations per year; 478 asthma-related deaths were recorded in 2024 (the most recent data), almost half in women aged over 75. Acute asthma can be life-threatening.

Asthma phenotypes include allergic asthma, non-allergic asthma, aspirin-exacerbated respiratory disease (AERD — around 7% of asthma, ~15% of severe asthma), asthma with obesity, adult-onset asthma, cough-predominant asthma, and asthma with persistent airflow limitation. Symptoms can be triggered by exercise, respiratory infections, airborne allergens (grass pollen, pets, house dust mite, moulds), airborne irritants, and some medicines.

History and examination

Ask about current symptoms (wheeze, breathlessness, chest tightness, cough), pattern (daytime and night-time, changes over weeks or years), triggers (exercise, viral infections, cold dry air, foods, medicines, allergens), home and work environment, smoking/vaping history (including cannabis) and smoke exposure, allergy history (atopic dermatitis, allergic rhinitis), and family history of asthma/allergies.

Examine the chest (auscultation) and upper respiratory tract, and look for features suggesting a comorbid or alternative diagnosis — allergic rhinitis, rhinosinusitis, nasal polyps, heart murmurs, crackles, or inspiratory wheeze (stridor).

Differential and comorbid diagnoses

Condition	Suggestive features
Bronchiectasis	Productive cough with a history of recurrent infections
Chronic cough / laryngeal hypersensitivity	Dry cough is the dominant symptom; throat-clearing; dysphonia; “scratchy” throat; triggered by talking, laughing, strong odours or smoke; may be associated with chronic rhinosinusitis or GORD
COPD	Onset >40yrs, smoking/dust exposure, recurrent chest infections, persistent breathlessness, family history of emphysema
Inducible laryngeal obstruction	Breathing difficulty triggered by strong smells, irritants, or exercise; throat tightness or voice change; may be associated with chronic dry cough; breathlessness worst at peak exercise; inspiratory wheeze (stridor) suggests a laryngeal or upper airway abnormality
Large airway stenosis	Breathlessness or wheeze
Pulmonary fibrosis	Breathlessness on exertion or dry cough; fine inspiratory crackles
Rhinosinusitis	Cough co-occurring with rhinosinusitis symptoms
ACE inhibitor-related cough	Cough is the dominant symptom
Dysfunctional breathing	Breathlessness, often irregular pattern; may be associated with hyperventilation (dizziness, light-headedness, tingling fingers)
GORD	Cough or chest tightness with symptomatic reflux
Heart disease	Chest tightness on exertion, dyspnoea on exertion or lying flat, basal crepitations
Recurrent respiratory infection	As clinically typical
Lung cancer	Persistent cough despite treatment, haemoptysis, chest pain, weight loss
Panic attacks	Breathlessness/chest tightness at rest or on minor exertion with anxiety
Poor cardiopulmonary fitness	Breathlessness on exertion, no other features
Pulmonary embolism	Sudden-onset dyspnoea; history of recent surgery or immobility

Spirometry and FeNO testing

Perform (or arrange) spirometry including bronchodilator responsiveness testing, with at least 3 manoeuvres each time. If spirometry isn’t available in the practice, refer to an accredited respiratory function laboratory and request both spirometry and FeNO — don’t delay treatment if indicated while waiting.

Bronchodilator responsiveness: measure FEV1 before and 10–15 minutes after a rapid-acting bronchodilator (e.g. salbutamol). A positive response (FEV1 increase ≥12% and ≥200 mL) confirms asthma if the clinical picture is consistent — but bronchodilator responsiveness testing alone does not distinguish asthma from COPD, and its absence does not exclude asthma (especially if the patient is currently asymptomatic).

FeNO ≥40 ppb supports an asthma diagnosis in a patient with suggestive signs/symptoms.

Before spirometry, withhold inhaled bronchodilators: ≥4 hours for salbutamol/terbutaline, ≥24 hours for formoterol/salmeterol, ≥36 hours for indacaterol/olodaterol/vilanterol, 36–48 hours for aclidinium/glycopyrronium/tiotropium/umeclidinium.

Making the diagnosis

Diagnose asthma if all of the following apply:

1. History of recurrent or persistent respiratory symptoms that vary in frequency and severity.
2. Signs and symptoms are unlikely to be due to an alternative diagnosis.
3. Variable expiratory airflow limitation and/or FeNO ≥40 ppb has been demonstrated.

If initial spirometry doesn’t confirm the diagnosis but clinical findings still suggest asthma, consider further testing — clinically important variation in FEV1 (≥20%) across separate visits, an exercise-induced FEV1 fall (≥12% and ≥200 mL), an FEV1 rise (≥12% and ≥200 mL) after a 4+ week ICS treatment trial, diurnal peak-flow variability >10%, or referral for bronchial provocation/challenge testing (airway hyperresponsiveness — contraindicated in pregnancy).

Offer referral to a respiratory physician if the diagnosis is unclear, or recent-onset symptoms appear triggered by workplace airborne irritants or sensitisers (occupational asthma).