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Asthma Diagnosis

Your doctor will perform a physical exam and ask you questions about your symptoms as well as about any other health problems you may have. This helps to rule out other possible conditions, such as chronic obstructive pulmonary disease (COPD) or respiratory infection.

Your doctor may also perform tests to diagnose asthma:

  • Spirometry: this test measures how much air you are able to breathe out after a deep breath and also how fast you are able to breathe out. This allows your doctor to estimate the amount of narrowing in your bronchial tubes.
     
  • Peak flow: this test uses a device called a “peak flow meter” that measures how forcefully you can breathe out. If your reading is lower than normal, this may be a sign that your lungs are not working as well as they previously have and that your asthma may be getting worse. Tracking peak flow readings helps both you and your doctor keep track of the progression of your asthma, and may help to identify things that make it worse.
     
  • Methacholine challenge: methacholine is a substance that can trigger asthma and cause mild constriction of the airways. If you have a reaction to methacholine, it is likely that you have asthma. This test can help diagnose asthma even when lung function tests are normal.
     
  • Provocative testing: this test measures the constriction of your airways before and after performing exercise or taking several breaths of cold air. The results will show if you have asthma that is triggered or aggravated by either exercise or cold air.
     
  • Allergy testing: these tests can be performed using a skin test or a blood test. They can show whether you are allergic to certain common allergens.
     
  • Imaging tests: chest X-rays or high-resolution computerized tomography (CT) scans can show structural abnormalities or other conditions in the lungs, such as infections.
     
  • Sputum eosinophils: this test examines the mixture of saliva and mucous (sputum) that you discharge while coughing. It looks for particular white blood cells (eosinophils), which are present when symptoms develop.

Asthma is classified according to how severe it is:

  • Mild intermittent: symptoms are mild and occur up to two days per week and two nights per month
  • Mild persistent: symptoms occur more than twice per week, though no more than once in a day
  • Moderate persistent: symptoms occur at least once per day and more than one night each week
  • Severe persistent: symptoms occur most days throughout the day and occur often at night