A diagnosis of asthma is based on the patient’s symptoms, medical history, a physical examination and laboratory tests to measure pulmonary (lung) function:

FEV1 testing
This uses a machine called a spirometer to measure the amount of air entering and leaving your lungs. In this test, you breathe in as much air as possible and then breathe out as fully as possible and the total amount of air breathed out is measured. If you have asthma symptoms, you will only be able to breathe out a small portion of the total amount during the first second and it will take you several seconds to breathe out the remaining air.

Other tests used in the diagnosis of asthma may include:

Bronchial provocation test
This consists of testing your lung function before and after inhaling either an agent that triggers asthma, or cold air. Another type of bronchoprovocation test which is used, particularly in people with exercise-induced asthma, is the exercise challenge test. In this test, your lung function will be measured before and after exercising, usually on a treadmill or exercise cycle.

Chest x-ray
Your doctor may want you to have a chest x-ray to rule out other possible causes of your breathing problems.

Allergy testing
Your sensitivity to a number of allergens may be tested by a simple and safe skin-prick test in which small samples of the suspected allergen(s) are tested on the skin, usually on the forearm, and the presence of a skin reaction is observed.

Blood tests
Blood tests can also be used to look for specific allergies. You will need to give a small sample of blood, which will be sent to a laboratory for testing.