Signs of airflow limitation variability

Positive bronchodilator reversibility test
Increase in forced expiratory volume in 1 second (FEV1) > 12% and > 200 mL from baseline 10–15 minutes after administering 200–400 μg albuterol or equivalent (more likely to be positive if bronchodilator is withheld before test: short-acting beta-agonists for at least 4 hours and long-acting beta-agonists for at least 15 hours before test)
High variability in peak expiratory flow (highest of 3 readings), performed twice daily for 2 weeks
Average daily diurnal variability > 10%
Significant increase in lung function after 4 weeks of anti-inflammatory treatment
Increase in FEV1 by > 12% and > 200 mL (or peak expiratory flow by > 20%) from baseline
Positive exercise challenge test
Fall in FEV1 of > 10% and > 200 mL from baseline
Positive bronchial challenge test
Fall in FEV1 from baseline of ≥ 20% with standard doses of methacholine or histamine, or ≥ 15% with standardized hyperventilation, hypertonic saline, or mannitol
Excessive variation in lung function between visits
Variation in FEV1 of > 12% and > 200 mL