Asthma can be diagnosed in a number of ways. Some of the main ways are:
Peak Expiratory Flow (PEF) test - To measure the flow of air out of the lungs. If, over a period of time, the morning and evening values vary by more than 15%, or treatment for asthma improves the readings by more than this value, this is indicative of asthma.
Lung function test - This is useful in assessing the breathing in more detail. It involves breathing into a machine which records the airflow and volumes during various breathing manoeuvres.
A reversibility test may be used to assess your response to a bronchodilator (reliever to open up your airways) such as salbutamol. In asthma there is usually a marked improvement in lung function measurements after a dose of medication.
Airway responsiveness or challenge tests - This highly specialised test is sometimes used to diagnose asthma when the diagnosis is not clear from the more simple tests mentioned above. It is carried out only in the hospitals and measures how your airways respond when they come into contact with a trigger.
Nitric oxide (FeNO) test - This test measures the amount of nitric oxide in your breath. When your airways are inflamed — a sign of asthma — you may have higher than normal nitric oxide levels.
Imaging tests - A chest X-ray and high-resolution computerized tomography (CT) scan of your lungs and nose cavities (sinuses) can identify any structural abnormalities or diseases (such as infection) that can cause or aggravate breathing problems.
Allergy tests - This can be performed by a skin test or blood test. Allergy tests can identify allergy to pets, dust, mould and pollen.
Tests can also be carried out to see if you are allergic or sensitive to certain substances known to cause occupational asthma. If important allergy triggers are identified, this can lead to a recommendation for allergen immunotherapy.