Tests for severe asthma

Tests help you and your doctor find out more about your severe asthma.

Health advice > Severe asthma > Diagnosing severe asthma

Find out about tests used to diagnose and monitor severe asthma, including tests to find out if you have other conditions that could be making your asthma worse.

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To find out more about allergy tests, peak flow and other lung function tests see our asthma tests page.

Why do I need extra tests for severe asthma?

You may have had tests for your asthma already. But if your doctor thinks you could have severe asthma, you’ll need extra tests to confirm it or to find out what else might be causing your symptoms or triggering your asthma. And if you do have severe asthma, you’ll need further tests to monitor symptoms and treatments.

The tests will help you and your specialist team find out if you have:

  • severe asthma or not
  • allergic or non-allergic severe asthma
  • other conditions that are causing your symptoms or stopping you from managing your asthma well.

Not everyone will need all of these tests. Your asthma specialist will explain which ones could be useful for you and why. They can also support you if you’re worried or nervous about any of the tests.

There may be some tests you need to do more than once to help your asthma specialist make the right diagnosis or monitor you closely.

If you don't like the idea of having lots of tests, remember they are there to help you manage your asthma better and hopefully get back some control over your symptoms.

Blood tests

A blood test is a quick and simple test that can give useful information about your general health and the type of asthma you have.

A blood test can help you and your specialist team know:

  • If you have high levels of allergic antibodies in your blood. This suggests your severe asthma is triggered mainly by allergy. Find out more about allergy tests and asthma.
  • If you have high levels of eosinophils in your blood. An eosinophil is a certain type of white blood cell responsible for inflammation in your body. High levels of eosinophils suggest eosinophilic asthma.
  • If your liver and kidneys are working properly. This shows if your body will handle certain types of severe asthma treatments and absorb them properly.
  • If your immune system is working well.
  • If you have low levels of vitamin D or low levels of iron (anaemia) which could be other possible causes of your symptoms.

Lung function tests

Lung function tests show how your lungs are working and how you’re breathing. They are very important tests to help diagnose asthma and to monitor it.

Spirometry test

A spirometry test measures how much air you can breathe out in a set time and how narrow your airways are. Spirometry tests can be used to monitor your asthma, especially if it’s not well controlled.

Your specialist may use spirometry alongside a bronchodilator reversibility test (BDR). This can show how well your medicines are working.  

Spirometry is also used alongside bronchial challenge tests.

Find out more about spirometry tests.

Lung volume test

A lung volume test shows the total size of your lungs. Your specialist may call it lung plethysmography.

A lung volume test measures how much air you can hold in your lungs. It can let your specialist team know if your lung condition is obstructive or restrictive. Asthma is obstructive, which means the lungs never empty completely.

If the test shows up problems with lung capacity, you’ll need other tests to see what the main cause of this is.

Results from a lung volume test vary depending on your age, gender, body size, and level of fitness.

Find out more about lung volume tests.

Gas transfer test

This test measures the amount of oxygen that passes from your lungs into your blood.

You may be asked to do this test as a way to monitor your severe asthma.

Find out more about the gas transfer test

Bronchial challenge tests

A bronchial challenge test works by deliberately challenging or provoking your airways. It is sometimes called a bronchoprovocation test or challenge test.

Challenge tests are done alongside spirometry tests.

You’ll be asked to breathe in a substance known to trigger a reaction in your lungs.

Not everyone can do bronchial challenge tests, but they can be a useful way to show how sensitive your airways are or how well your medicines are working to make your airways less sensitive. Find out more about bronchial challenge tests.

You may also be asked to do an exercise challenge test to see your breathing and heart rate during exercise Find out more about exercise challenge tests

Validated questionnaires

Your specialist team will use sets of questions, known as validated questionnaires, to help understand more about your condition and what could be making it worse.

These are mostly questions about your symptoms and how well you’re controlling your asthma. But they could also be about your breathing patterns and your mental health. 

Asthma control questions

Asthma control questions are a set of standard questions to find out about your asthma symptoms and how well they are controlled. It’s a way to get specific answers to how your symptoms are now.

Questionnaires include the Asthma Control Test (ACT) and the Asthma Control Questionnaire (ACQ), and the RCP 3 Questions.

Many severe asthma clinics will use other questions too. These may look at the impact of symptoms on your life.

Find out more about symptom control questions.

Hyperventilation questionnaire

Your specialist team may use this questionnaire if they think you’re breathing too fast (hyperventilating). Hyperventilation and other problems with breathing patterns can make asthma symptoms worse.

The hyperventilation questionnaire most often used by the NHS is the ‘Nijmegen Questionnaire’.

It asks you how often you have had symptoms such as faster or deeper breathing, dizzy spells, blurred vision, and palpitations and uses points for each answer.

Your specialist can tell from your scores if you may be hyperventilating.  

Studies suggest people who hyperventilate may benefit from physiotherapist-supervised breathing techniques such as the Papworth method and Buteyko Breathing Technique. Breathing techniques can improve symptoms and quality of life for some people with asthma.

Depression and anxiety questionnaires

These questionnaires are used to find out how having asthma is affecting you emotionally.

Understandably, people with severe asthma often experience anxiety or depression, or both, often because of the challenges around living with a long-term condition where symptoms are affecting daily life.

It’s important that your asthma specialist and healthcare team have a good understanding of how you’re feeling, so they can give you the support you need.

Often, identifying and treating depression and anxiety can have a big impact on someone’s symptoms and quality of life. 

X-Rays and CT scans

You may have both tests together to give a more complete picture of your lungs. A CT scan gives more detail than an X-ray. 

Chest X-ray

Chest X-rays give an image of the inside of your chest. They are used to check that there isn’t anything else going on in your lungs, which could be causing your symptoms or making your asthma symptoms worse. This could be a blockage or scarring in your lungs or an infection like pneumonia.

CT scan 

A computerised tomography (CT) scan uses X-rays and computers to give a detailed 360-degree image of the inside of your lungs.

A CT scan is mostly used to confirm or rule out other conditions that could be making your symptoms worse, such as bronchiectasis, fibrosis, or pneumonia.

Some clinics will also perform a CT scan of your nose and sinuses. This is because for many people inflammation in the nose and sinuses (the upper airways) can make asthma symptoms worse.

Find out more about X-rays and CT scans.

FeNO (Fractional Exhaled Nitric Oxide) tests

A FeNO test is most often used as a test to diagnose asthma. But it may be used in a specialist centre to monitor your severe eosinophilic asthma.

FeNO is useful for helping your healthcare team prescribe or adjust the dose of your medicine or change your treatment to help you stay well with asthma.

You can find out more about the FeNO test here. 

Sputum induction test

A sputum induction test involves breathing in different concentrations of slightly salty water through a nebuliser and then coughing them up to produce a sample that can be analysed in a laboratory.

You may be asked to do a sputum induction test if your specialist team wants to know more about what’s causing the inflammation in your airways.

A sputum induction test shows what cells are present. This can help the specialist know what type of asthma you have and what treatments might work best for you. For example, high numbers of eosinophils (a type of white blood cell responsible for inflammation) suggest you have eosinophilic asthma. Knowing this can help your specialist team work out the best treatments for you, for example, biologic treatments


Bronchoscopy involves passing a thin, flexible tube down your throat and into your airways. The tube has a light and a camera on the end to allow your asthma specialist to see right into your airways. You’ll be given a sedative beforehand and the back of your throat will be numbed, so it’s less uncomfortable.

A bronchoscopy allows your asthma specialist to see inside your airways and to take a small sample of phlegm or tissue for examination. 

The results will help your asthma specialist rule out other conditions that could be making your asthma symptoms worse.

Find out more about bronchoscopy.

Nasal endoscopy

A nasal endoscopy test uses a thin microscope to examine the inside of your nose and sinuses and throat. It’s usually done in an outpatient clinic.

Your specialist team may recommend this test if they think problems in your nose and sinuses may be triggering some of your symptoms and making your asthma worse.

Because conditions that affect your nose and nasal passages can trigger asthma symptoms, the results of this test can show whether or not you need treatment for your sinuses to help control your asthma symptoms.

Tests for acid reflux

Acid reflux is when acid leaks out of your stomach and up into your oesophagus (the tube that takes food to the stomach) causing an uncomfortable burning sensation in your chest (heartburn).

Stomach acid irritates your airways and causes inflammation, which can make your asthma worse.

If the tests show that you have acid reflux, your team can treat this alongside your severe asthma. Although it’s not yet clear whether treating acid reflux improves asthma symptoms, there is some evidence to say it might improve them for some people.

24-hour pH monitoring

This involves passing a thin tube up your nose and down your throat. The tube has a sensor to measure the acidity level (pH) in your throat.

The tube may be attached to a recording device that’s worn on your waist. Every time you become aware of symptoms, you’ll be asked to press a button on the device and write down your symptoms in a diary.

Manometry test

A manometry test involves passing a small tube containing pressure sensors up your nose and down into your oesophagus. 

The test shows how well the ring of muscle at the end of your oesophagus is working by measuring the pressure in your oesophagus.

The results will help your asthma specialist to rule out or confirm that acid reflux or gastro-oesophageal reflux disease (GORD) is a cause of your asthma symptoms or is making your asthma worse.

Bone density scan (DEXA)

A bone density or DEXA scan uses X-Rays to see how dense or strong your bones are. DEXA stands for ‘dual-energy X-ray absorptiometry.’

If your specialist team thinks you’re at increased risk of thinning bones - for example, because you’ve been on long-term steroids - you should be offered a DEXA or bone density scan.

This test may be offered as an extra monitoring test if you’re at risk.

Find out more about DEXA scans.


ECG stands for electrocardiogram. An ECG is a simple test that uses sensors attached to your chest to check the electrical signals your heart produces each time it beats. An ECG is used to check your heart’s rhythm and electrical activity.

Depending on your age, medical history, and symptoms your specialist may decide to use this test to see whether your heart is triggering or causing some of your severe asthma symptoms. 

An ECG test checks whether your heart is healthy enough to prescribe certain medicines. It can also show up any other possible causes of your asthma symptoms, such as an irregular heartbeat, an enlarged heart, or previous damage to your heart muscles.


For more support about tests for severe asthma call our Helpline team on 0300 222 5800 (9am - 5pm; Mon - Fri). Or you can WhatsApp them on 07378 606 728.


Last updated April 2022

Next review due April 2025



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