Using a machine called a spirometer, the amount of air you breathe out and how quickly you can exhale are recorded. If the measurements are below normal for a person your age, it may be a sign that your airways are narrowed by asthma.

Peak flow test

Measures how fast you can blow air out of your lungs in one breath (your peak expiratory flow). Sometimes, this test is also conducted by you in your home or work to see if the triggers in those environments are causing your symptoms.

Reversibility test

Sometimes you or your child is given a medicine to open up the airways (a reliever inhaler) and the spirometry test is performed again. If you or your child’s symptoms have improved, then you or your child may have asthma.

Challenge tests

Sometimes a very small amount of a known trigger is inhaled or taken by mouth to diagnose asthma. This test measures how you react when you breath in methacholine, a known substance that deliberately irritates and constricts the airways slightly. If you have asthma, you will respond to methacholine.

Testing airway inflammation

These tests help determine the presence and degree of inflammation in your airways through a mucous sample or a test to measure the amount of nitric oxide gas in your breath. A high level of nitric oxide can be a sign of airway inflammation—one sign of asthma.