If you have symptoms that could be due to asthma, your doctor will:

  • ask about the symptoms
  • ask about your general health, including allergies and hay fever
  • do a physical examination (e.g. listen to your chest and check inside your nose)
  • consider other possible causes of the symptoms
  • arrange a spirometry test, either in the doctor’s office or in a testing clinic.

There is no single test for asthma. Doctors make the diagnosis of asthma when a person has breathing symptoms that are typical of asthma, usually after breathing tests. Breathing tests measure how easily air flows in and out of the lungs, and whether airflow varies.
Airflow can vary in healthy people too (e.g. when someone has a cold their lungs may not work as well as usual). But for people with asthma, there is a much bigger difference between their personal best and worst lung performance.

Your lung function (how well your lungs are working) is tested using a spirometer machine. You blow into a tube as forcefully as you can for a few seconds. The spirometer measures the amount of air pushed through the tube, as well as other lung measurements.

If your symptoms only or mainly happen at work, your GP may refer you to a specialist. If you have been diagnosed with asthma in the  past and you visit a new doctor, the diagnosis may need to be rechecked. This may involve changing or reducing medication for a few weeks and doing the spirometry test again.

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