A 12% increase in FEV1 after bronchodilator means your airflow improved following the inhaler used during spirometry.

For a significant positive bronchodilator response in adults, the usual traditional criterion is:

Formula:

[ % \text{ change} = \frac{\text{Post-FEV1} - \text{Pre-FEV1}}{\text{Pre-FEV1}} \times 100 ]

Example: pre-FEV1 2.00 L, post-FEV1 2.24 L:

[ (2.24-2.00)/2.00 \times 100 = 12% ]

If the increase is also 200 mL or more, it supports reversible airway narrowing, which can occur with asthma. It does not by itself diagnose asthma. The FEV1/FVC ratio, symptoms, test quality, and clinical history also matter. ERS asthma guideline uses the ≥12% and ≥200 mL criterion. Textbook support: Murray & Nadel's Textbook of Respiratory Medicine, lines 420-422.