How is asthma diagnosed?

There is no single test for asthma. Doctors make the diagnosis of asthma when a person has breathing symptoms typical of asthma that come and go, and there is also evidence that sometimes air does not flow in and out of their lungs normally.

Airflow can vary in healthy people too (e.g. when someone has a cold their lungs may not work as well as usual). But people with asthma have a much bigger difference than healthy people between how their lungs work at their best and at their worst.

How well the lungs work (lung function) 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 lung capacity and other measurements. Most children over 6 years old can do this asthma test, but is not used for preschool children or adults with certain medical conditions.

If you or your child may have asthma, your doctor will:

  • ask about the symptoms
  • ask about general health, including whether you (or other family members) have allergies like eczema or hay fever
  • do a physical examination (e.g. listen to the chest, check inside the nose)
  • consider other possible causes of the symptoms
  • arrange a spirometry test (for adults and children aged 6 years and over).

If you or your child has a cold or flu, spirometry should be repeated later when you are well.

Sometimes it is not possible to be sure whether a young child has asthma or not, until they are old enough to do the spirometry test. Wheezing and coughing are very common in little children, even if they do not have asthma. Doctors often try out an asthma medicine for a few weeks (e.g. ask you to give it just when your child has symptoms) and arrange a check-up to see how it worked.

Before making the diagnosis, your doctor may order other tests or refer you or your child 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.

Before you visit your doctor

  • Video (or audio -record) the wheezing on your phone, if possible.
  • Write down how often the symptoms happen in the day or night, and which symptoms.
  • Try to remember whether symptoms change over time (during a day, week or year), and whether anything makes them worse (e.g. exercise, colds and flu, allergies).
  • For children, keep a note of whether wheezing only happens over a few days from time to time (e.g. when the child has a cold) or at any time (e.g. coughing and wheezing while playing or laughing). Watch your child’s chest when wheezing and tell your doctor if it looks different from breathing when there is no wheezing.

More information

  • Talk to your doctor or pharmacist 
  • Contact your local Asthma Foundation on 1800 645 130 or

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