What percentage of change in Forced Expiratory Volume in 1 second (FEV1) after bronchodilator administration is considered indicative of asthma?

Bronchodilator Response Criteria for Asthma Diagnosis

An increase in FEV1 of ≥12% and ≥200 mL from baseline after bronchodilator administration is considered diagnostic of asthma. 1, 2

Diagnostic Criteria for Bronchodilator Response

The European Respiratory Society (ERS) guidelines establish clear criteria for interpreting bronchodilator response in spirometry:

• Primary criteria: Increase in FEV1 and/or FVC ≥12% and ≥200 mL from baseline values 1, 2
• This threshold has good specificity (90-98%) but lower sensitivity (35-36%) for asthma diagnosis 1
• The response should be measured 15 minutes after administration of a short-acting bronchodilator 1, 2

Standardized Testing Protocol

For accurate and reliable results, follow this protocol:

1. Perform baseline spirometry to measure pre-bronchodilator FEV1 and FVC
2. Administer 400 μg of short-acting β2-agonist (e.g., salbutamol/albuterol) via metered-dose inhaler with spacer 1, 2
3. Wait 15 minutes
4. Repeat spirometry measurements
5. Calculate both percentage change and absolute change in milliliters

Interpreting Results

Positive Response (Suggestive of Asthma)

• FEV1 increase ≥12% AND ≥200 mL from baseline 1, 2
• FVC increase ≥12% AND ≥200 mL from baseline (also considered significant) 2

Important Considerations

• Bronchodilator responses tend to be higher in patients with lower baseline FEV1 or FVC values 1
• Patient-based studies show higher bronchodilator responses compared to general population studies 1
• A negative bronchodilator response in the laboratory does not exclude asthma or preclude clinical benefit from bronchodilator therapy 1, 2

Alternative Assessment Methods

When spirometry with bronchodilator testing is inconclusive:

1. Peak Flow Monitoring: A variability of >10% in adults and >13% in children over 1-2 weeks is suggestive of asthma 1

2. Post-Controller Therapy Assessment: In adults, if FEV1 improves by >12% and >200 mL after 4 weeks of anti-inflammatory controller therapy (e.g., inhaled corticosteroids), this supports an asthma diagnosis 1

Common Pitfalls to Avoid

1. Ignoring FVC changes: An isolated increase in FVC (≥12% and ≥200 mL) is also a sign of bronchodilation 2

2. Relying solely on laboratory testing: The absence of bronchodilator response in a single test does not exclude asthma 1, 2

3. Using fixed thresholds without context: Bronchodilator response depends on age, sex, height, and degree of airway obstruction 3

4. Overlooking clinical symptoms: Diagnosis should incorporate both objective measures and clinical presentation 1

5. Administering bronchodilators too soon before testing: Short-acting β-agonists within 4 hours or long-acting β-agonists within 15 hours of testing can lead to false-negative results 1

The 12% and 200 mL threshold has been established as the standard diagnostic criterion, though some research suggests that a less stringent improvement might be applicable in children 4. Nevertheless, current guidelines maintain the 12% threshold for both adults and children 1.