A reversibility test is made to distinguish asthma from other causes of obstructive lung disease.
A reversibility test in spirometry usually follows the following steps:
- spirometry test (with at least 2 reproducible flow volume loops)
- intake of a fast acting bronchodilator (often Salbutamol) through inhalation
- 15 minutes pause
- a second spirometry test (with at least 2 reproducible flow volume loops)
Now we have 2 sets of flow-volume loops: pre-medication and post-medication.
FEV1 rises at least 15% after intake of a bronchodilator in case of asthma
In case of asthma, a significant improvement in FEV1 will be seen after the intake of the bronchodilator. A rise in FEV1 of at least 15% is diagnostic for asthma.
If FEV1 has risen less than 15% after the intake of the bronchodilator, the obstruction is likely to be caused by another pathology (like COPD) and other tests will be necessary to make a definite diagnosis. Asthma is still possible though!