Tests to diagnose and monitor asthma

There are several different tests used to help diagnose and monitor asthma

How is asthma diagnosed?

Asthma nurse Sue explains how asthma is diagnosed by a nurse or GP - including the types of asthma tests that are used

Video: How is asthma diagnosed?

Asthma nurse Sue explains how asthma is diagnosed by a nurse or GP - including the types of asthma tests that are used
Transcript for 'How is asthma diagnosed?'

0:00 If you or your GP suspect that you may have asthma, they will start off by making sure they've got an accurate

0:07 history of your symptoms, your lifestyle, any past medical history, and also family history - to see if asthma is a

0:16 possibility. To help with diagnosing asthma, it's important to do some tests, to find out exactly how well your lungs are working, and to be able to identify

0:27 whether they're inflamed, which is a key aspect of asthma. One of the tests you'll be asked to do is to blow into a peak flow meter. This is a child's version.

0:37 It's very difficult to diagnose asthma in children, but once they're about 5 to 6 years of age they may be able to blow into one of these. Blowing into one of

0:47 these will give us a reading of how fast you can blow your air out. You may be asked to take this home with you and to record peak flow readings over several

0:59 times a day to get a variation, and that will help the doctor actually diagnose whether you've got asthma or not. You'll also be asked to do a spirometry test.

1:09 This measures lung function; how much your lungs actually can hold, and how quick you can blow your air out. Now this takes a little bit more time, and you would have to attend the surgery to have

1:22 this done. You may be at the surgery between 20 minutes and an hour depending on the test. You'll be asked to blow into this spirometer. After the test you will have four puffs of a blue reliever

1:37 inhaler, through the spacer, and after 20 minutes you'll be expected to do the test again. And these results will show us, compared with your age and your

1:48 height, whether they are normal or less than predicted. It's important to remember that you may have to do these tests several times to ensure that we

2:01 get an accurate diagnosis. Asthma can vary day to day, week to week, month to month, so you may get an abnormal test one day, and it might be normal

2:13 another. Even if all the results from the tests come back as normal it doesn't exclude asthma, and your GP may decide to put you on a trial of treatment which

2:24 you would have to take for about six, eight weeks and see all your symptoms got better

If you're having symptoms like cough, wheeze, breathlessness or a tight chest your GP may refer  you to a hospital or clinic for further tests to see if you have asthma.

There are several tests that help to confirm an asthma diagnosis. Some are also used to monitor your asthma once you've been diagnosed.

These tests help to show if your airways are narrow or inflamed, and how your lungs respond to medicine.

They are the best way to confirm or rule out asthma. And if you do have asthma they can help your GP decide the best treatment for you.

It’s important to remember that if your results come back normal after a test, it doesn’t completely rule out asthma.

Because asthma symptoms can vary over time, it could just mean that on the day of the test your airways were not as narrow and inflamed. You may need to take the test more than once, or take a combination of tests, to help your GP make the right diagnosis. 

Asthma UK's in-house GP, Dr Andy Whittamore, explains: "If you have one negative test, of all the various ones that are currently available, or you don’t have symptoms, it doesn’t mean you don’t have asthma." Read Dr Whittamore’s blog post ‘Get the real story on asthma diagnosis’.

You may also be given an allergy test if your GP thinks your asthma is triggered by a specific allergen (a substance that causes an allergic response).

Your GP, asthma nurse or consultant will explain which tests are suitable for you or your child (tests for asthma are usually offered to children aged five and above). You can find out more on our page Getting an asthma diagnosis for your child.

As well as the tests listed here, there are some other tests which asthma specialists might use to help diagnose and monitor severe asthma.

If you want to talk about your diagnosis, or your asthma test results, you can call our Helpline on 0300 222 5800.  It’s open Monday to Friday, 9am to 5pm.

Peak flow

What is it?

The peak flow test (Peak Expiratory Flow test or PEF) is a lung function test to measure how fast you can breathe out.

You take a full breath in, then blow out as fast as you can into a small, hand-held plastic tube called a peak flow meter. The measurement taken is called your peak flow.

Your GP will get you to repeat this test a few times and then they will note down your best reading.

When is it used?

Your GP or asthma nurse might use a peak flow test to help see how open your airways are. They often use this test when you first tell them you're experiencing symptoms that might be asthma.  They may ask you to keep a peak flow diary for 2-4 weeks to help confirm an asthma diagnosis.

Your GP or asthma nurse should do a peak flow test at every annual asthma review as part of their routine checks.

This test is also useful for monitoring your asthma using a peak flow diary alongside a symptom diary and your asthma action plan.

You can buy, or get a prescription for, a peak flow meter and your GP or asthma nurse will show you how to do the test yourself at home.

What do the results show?

Peak flow scores show how well your lungs are working. Scores will vary depending on your age, your height and whether you're a man or a woman. 

Although your peak flow reading may be different in the morning or at night, it's the pattern your scores make that's important, rather than one score on its own. Most people have a best peak flow reading so you'll be able to see when your reading goes up and down.

Keeping track of your peak flow while monitoring your symptoms can help you spot when your asthma is getting worse and when you need to use your reliever inhaler (usually blue) or get medical help. 

Read our peak flow test page to find out more about using peak flow to help you stay on top of your asthma, and warn you of an asthma attack.


What is it?

This is a breathing or ‘lung function’ test. It’s one of the most common tests people with asthma, or people who are being tested for asthma, are given.

Your GP or asthma nurse will ask you to take a deep breath and then breathe out as fast as you can and for as long as you can, through a mouthpiece linked to a ‘spirometer’. You will have to blow a few times so your GP or asthma nurse can get an accurate result.

Once they have an accurate result, you may then be given a bronchodilator (reliever) medicine to open up your airways. You'll be asked to wait 15-20 minutes then blow into the machine a few times again.

This is to see whether there’s a big change in your airways after taking the medicine. If they become much less narrow, it could be a sign that you have asthma.

When is it used?

Spirometry is used to help your GP or asthma nurse work out how likely it is that you have asthma. For best results, it’s usually done before you start taking any preventer medicine. 

Your GP may also ask you to do a spirometry test at your annual review to see how well your lungs are functioning, and how well your medicines are working.

What do the results show?

A spirometer measures how much air you can breathe out.

By comparing your results to measurements that are considered ‘normal’, your GP or asthma nurse can work out if the amount of air you’re able to breathe out is less than the expected range for your age, height and ethnicity. The test shows if your airways are narrow or inflamed.  

Your GP will also be able to see whether your airways have responded to the bronchodilator medicine. If they have, it’s likely you have asthma.

This test can also help your healthcare team see if your symptoms might be caused by another lung condition, such as chronic obstructive pulmonary disease (COPD).

Airways responsiveness test

What is it?

This highly-specialised test is carried out in hospital. It measures how your airways respond to asthma triggers.

You’ll be asked to breathe in a substance (histamine or methacholine) that may irritate your airways. This can cause the airways to become inflamed and narrower, and trigger asthma symptoms.

Don’t worry – if any asthma symptoms are triggered, your specialist will be on hand to reassure, monitor and treat you if necessary.

When is it used?

This test will probably only be used if the results of your spirometry test didn’t give your GP or asthma nurse a clear picture of whether or not you have asthma, and you still have unexplained symptoms.

What do the results show?

Your asthma specialist can use the results of this test to work out if and how your airways react to substances that can trigger asthma symptoms. They can then use this information to decide which asthma treatments are likely to work for you.

If you don’t have a reaction to the substances you breathe in, it’s less likely you have asthma.

FeNO testing

What is it?

If you’re given a ‘Fractional Exhaled Nitric Oxide’ test (FeNO), a hand-held machine is used to measure your levels of nitric oxide when you breathe out.

Nitric oxide is produced in your lungs when your airways are inflamed because you’re allergic to something you’ve breathed in.

A high level of nitric oxide in the air you breathe out can be a sign that you have inflamed airways and that you have asthma.

When is it used?

FeNO testing is used to help confirm an asthma diagnosis.

If you’ve been diagnosed with asthma and you’re using your preventer inhaler correctly, but still have asthma symptoms, your GP, asthma nurse or specialist may ask you to do a  FeNO test (usually as well as a spirometry test). This helps them work out the type of asthma you have.

As an alternative to this FeNO test, your specialist may take a sample of mucus (phlegm) to test for inflammation.

What do the results show?

The FeNO test checks for inflammation in your airways and tells a specialist if you have allergic or non-allergic asthma.

This is useful for helping your specialist to adjust the dose of your medicine or change your treatment to help you stay well with asthma.

Allergy tests

What is it?

There are two main allergy tests people with asthma might have: a blood test (known as a ‘specific IgE’ or ‘RAST’ test) and a skin-prick test where your skin is pricked with a tiny amount of the allergen you think you might be allergic to.

When is it used?

If your GP thinks your asthma symptoms may be triggered by certain allergens, such as dust mites, mould, pollen or certain foods, you may be referred to a specialist for allergy tests.

An allergy test will be able to pinpoint exactly what you’re allergic to so you can put the right steps in place to manage your asthma well.  

What do the results show?

A skin prick test is most commonly used allergy test.

Your specialist will prick your skin with tiny amounts of the suspected allergen(s) and look for signs that your skin becomes itchy, swollen and red. You should get the results of your skin prick allergy test within about 20 minutes.

If you have a blood test the results will show your GP how many IgE antibodies in your blood have been produced by your immune system in response to a suspected allergen.

The results may show that your asthma is triggered by many different types of allergens – some you may not have been aware of. It might take a couple of days to get the results of your blood test. 

If the tests show that you’re allergic to a specific thing, talk to your GP or asthma nurse about how to avoid it, if possible, or manage it.

For example, if you’re allergic to a certain type of tree pollen, you can talk to your GP, asthma nurse or pharmacist about which hay fever medicines might be suitable for you to take during the months that pollen is in season.

Last updated November 2016

Next review due November 2019