There is no single test for asthma. To properly diagnose asthma, your doctor will ask you or your child several questions about symptoms, medical history, and risk factors and perform a physical exam to rule out any other possible conditions. A number of diagnostic tests are available to help diagnose asthma.


Spirometry is a lung function test that measures how much air you can inhale and exhale and how much air you can exhale in one second. Below-normal results can indicate airway obstruction. Your doctor may then administer medication and repeat the test to see whether there is improvement.

Bronchial Challenge Test

During a bronchial challenge test, a known asthma trigger—methacholine or histamine—is inhaled to cause the airways to constrict. A spirometer is then used to measure the subsequent lung function. If you react to the trigger to a certain level of sensitivity, you likely have asthma. This test is also called a methacholine challenge test or a histamine challenge test.

Peak Flow

A peak flow meter can determine your peak expiratory flow rate (PEFR), a measure of lung function. This is often a self-administered test for monitoring asthma, as the peak flow meter is easy to use at home.

Nitric Oxide Test

High levels of nitric oxide in your breath could mean that your airways are inflamed, which is a common sign of asthma. The nitric oxide test involves blowing into a mouthpiece connected to a machine that measures the amount of nitric oxide in your breath.

Chest X-Ray

A chest x-ray will allow your doctor to see inside your chest and examine your lungs. While it may not enable a specific diagnosis of asthma, it may help rule out other factors that might be affecting your breathing – such as a broken bone, an obstruction, or conditions such as pneumonia or bronchitis.