Diagnosing asthma can be difficult, since the symptoms are often similar to those of other respiratory conditions or heart disease. A diagnosis is usually based on a description of your symptoms, a complete medical history, and a physical examination. Diagnostic tests for those 6 years of age and over include pulmonary (lung) function tests (PFTs, for short) and challenge tests.

PFTs (pulmonary function tests) are a group of tests that are used to measure the function of the lungs. The most common PFT is a spirometry test, which uses a device called a spirometer to measure the amount and rate of air passing in and out of your airways. Another test that measures lung function is peak flow examination. This test uses a peak flow meter to measure the rate at which you breathe out air. Peak flow meters can be used at home to monitor your asthma.

Challenge tests are tests designed to trigger asthma symptoms in people with asthma. This may be tried if your PFTs are normal but asthma is still suspected. You will be asked either to inhale a substance or to exercise to try and cause the airways to narrow. Afterwards, you'll be asked to retake the spirometry test to see how your airways reacted.

Other tests may be done to rule out other conditions that may cause similar symptoms.