Testing for asthma

Once your child is old enough, they can do asthma tests to help confirm asthma

When can my child be tested for asthma?

Usually, once a child is over five years old, they’re more able to do asthma tests to confirm an asthma diagnosis.

Some children over five still cannot do tests well enough to get useful results. Try not to worry if this is the case for your child. Your GP can continue to treat them for ‘suspected asthma’ based on their symptoms and history. And your child can try the tests again in a few months or a year.

Will my child’s ‘trial of treatment’ affect the results?

Ideally, to get a true picture, your child would be tested for asthma before starting treatment with a preventer inhaler, but this is not always possible.

Your child may need to stop taking treatment for a short time before any tests, to get useful results. This is because, if your child’s been taking regular preventer medicines, the tests will show improved lung function.

What will the tests show?

Up until now, you may have been told to ‘watch and wait’. Or your child may have been given asthma medicines to try as part of a ‘trial of treatment.’

The time you have been waiting for tests is still useful. It can show how likely it is that your child has asthma. Once your child is ready for asthma tests, those tests, along with your child’s symptoms or response to treatment while you’ve been waiting, and their medical history, will help confirm or rule out asthma.

Asthma tests can show:

  • If your child’s lung function is better or worse, and if it varies from day to day, or from appointment to appointment, or due to treatments. The more it varies between good lung function, and not so good, the more likely it is to be asthma.
  • If your child’s airways are blocked, and how well they respond to asthma treatment.
  • If your child has inflammation in their airways due to allergy. This can support a diagnosis.
  • If it’s more likely to be something else, not asthma.

A single test is not enough to diagnose your child with asthma

There’s no single test for asthma. Your child’s GP may need to do some different tests. And tests on their own are not enough to confirm a diagnosis. Your child’s symptoms, how often they get them, alongside family history, are an important part of the diagnosis puzzle.

If the GP thinks it’s likely your child has asthma, perhaps because of their symptoms, or because of the results of a trial of treatment, they will want to use tests to confirm what they suspect already.
All the pieces of the puzzle - symptoms, signs, family history, and tests - need to come together to confirm your child has asthma.

What asthma tests are used for children?

There are three main tests used for children over five:

  • Spirometry
  • Fractional Exhaled Nitric Oxide test (FeNO)
  • Peak flow

If your child cannot do the tests well enough to get useful results, they can continue a trial of treatment, and watch, and try again in 6 to 12 months.


Your child will probably do a spirometry test first. This is to show if their airways are blocked and narrow. Your child will breathe into a mouthpiece as fast and as hard as they can, and for as long as they can, to measure how well their lungs are working.

If their airways are blocked and narrow, the GP will see how your child responds to reliever medicine before taking the spirometry test again.

Reliever medicine opens the airways. If the follow-up test shows that your child’s airways are less blocked, it means they have responded well to the reliever treatment, and asthma is likely.

Spirometry can be unreliable in children. Your child’s GP may suggest a FeNO test if they are still not certain of an asthma diagnosis because the spirometry was normal. Or because your child’s airways were blocked but did not respond to the reliever medicines.


A FeNO test is where your child breathes out a long steady breathe into a FeNO machine. The machine measures inflammation in their airways. It helps to show if your child has allergic asthma.

A positive result shows asthma is more likely. But a negative test cannot rule out asthma for sure.

If your child’s GP is still not certain of an asthma diagnosis, after their spirometry, and FeNO tests, they may suggest monitoring your child’s peak flow at home for a few weeks.

Peak flow

A peak flow test is when your child blows into a small plastic tube called a peak flow meter. This measures how fast they can breathe out.

Peak flow readings taken over a few weeks can show how your child’s lungs are working, and if this varies from one reading to the next.

Peak flow can sometimes be useful where there is still uncertainty after spirometry and FeNO tests. But on its own, peak flow is not a reliable test for diagnosing children. And results can be affected by any preventer treatments your child is taking as part of a trial of treatment.

Peak flow testing can be useful after a diagnosis for some children, especially those with difficult or severe asthma. Then it can show their response to treatment or be used as part of their asthma action plan.

When will I get a confirmed diagnosis for my child after tests?

How soon your child will get a confirmed diagnosis depends on how well your child has been able to perform the tests, and how well they have got on with any asthma treatments tried.

Diagnosis of asthma will be confirmed once your child’s GP has all the pieces of the puzzle they need:

  • Your child has asthma symptoms that come and go.
  • Tests showed blocked airways, but reliever medicines helped them.
  • Tests for allergic asthma came back positive (though not for all children)
  • Peak flow measurements showed lung function varied over time.

If tests still do not clearly confirm an asthma diagnosis, but your child is still having symptoms, their GP should review symptoms and re-test in six weeks.

Depending on their results, if asthma is not confirmed, your child may be referred to a specialist for more assessments, or to consider different diagnoses.

It’s important to confirm a diagnosis with tests.

Even if your child is getting on well with asthma treatments, it’s important to take them for tests once they are old enough to confirm they have asthma to make sure they’re not taking asthma medicines unnecessarily, or taking more medicines than they need. It’s also important to make sure other things have not been missed.

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