Which pulmonary function test finding supports a diagnosis of asthma?

• A. Improved by 12% in FEV1 after SABA
• B. 20% worsening on provocation testing
• C. No change after bronchodilator
• D. 30% improvement on baseline spirometry

Answer: (A)

Asthma shows reversible airway obstruction, meaning the airflow limitation improves with a bronchodilator. The most informative test finding is a measurable rise in FEV1 after inhaling a rapid-acting bronchodilator. A gain of about 12% (and typically at least 200 mL) from baseline after SABA strongly supports a diagnosis of asthma because it demonstrates reversibility of the obstruction.

Worsening on provocation testing reflects bronchial hyperresponsiveness, which can be present in asthma but does not alone prove reversibility. No change after bronchodilator argues against reversible obstruction, and a large improvement on baseline spirometry without testing bronchodilator effect isn’t a standard diagnostic criterion. The 12% improvement after SABA best fits the pattern of reversible airway obstruction characteristic of asthma.