Tests to Measure Lung Function
Spirometry. This test measures the narrowing of your bronchial tubes by checking how much air you can exhale after a deep breath, and how fast you can breathe out.
Peak flow. A peak flow meter is a simple device that can be used at home to help detect subtle changes before you notice symptoms. If the readings are lower than usual, it's a sign your asthma may be about to flare up. Your doctor will give you instructions on how to track and deal with low readings.
Lung function tests often are done before and after taking a bronchodilator to open your airways. If your lung function improves with use of a bronchodilator, it's likely you have asthma.