Answers to frequently asked questions about asthma.
Asthma is a heterogeneous disease, usually characterized by chronic airway inflammation. It is defined by the history of respiratory symptoms, such as wheeze, shortness of breath, chest tightness and cough, that vary over time and in intensity, together with variable expiratory airflow.
The diagnosis of asthma is based on characteristic variation in respiratory symptoms, and evidence of variable expiratory airflow from lung function testing. More than one test may be needed.
The most common lung function test is bronchodilator responsiveness (“reversibility”) testing, with lung function measured before and 15 minutes after giving a bronchodilator such as salbutamol (albuterol). If spirometry is not available, peak expiratory flow (PEF) should be used, instead of relying on symptoms alone. Other tests to confirm the diagnosis include bronchial challenge tests, which are available in specialist centers.
If possible, confirm the diagnosis of asthma before starting inhaled corticosteroid (ICS)-containing treatment, as it is often more difficult after treatment is started. However, in cases of clinical urgency, start treatment immediately, and review the patient’s response.
The GINA 2025 report provides additional advice to help confirm the diagnosis of asthma, including for patients already on treatment, the elderly, patients with cough as the only symptom (including cough variant asthma), and patients in low-resource settings.
What’s new in GINA 2025 about diagnosis of asthma? In patients with typical asthma symptoms, if lung function testing is not available or results are normal, elevated fractional exhaled nitric oxide (FeNO) or elevated blood eosinophils can support the diagnosis of Type 2 asthma. However, they may be elevated in non-asthma conditions, and lower levels do not rule out asthma.
To read more about Diagnosis of asthma, see Section 1 of the GINA 2025 report, particularly the following resources:
- Box 1-1. Diagnostic flow-chart
- Box 1-2. Diagnostic criteria
- Box 1-3. Differential diagnosis of asthma
Box 1-4. Confirming the diagnosis of asthma after treatment has been started.