Tests for severe asthma

To confirm or rule out a diagnosis of severe asthma you may need some extra tests.

Health advice > Severe asthma > Diagnosing severe asthma

At the specialist asthma clinic

If you’re taking your asthma medicines exactly as prescribed and using the right inhaler technique, but you’re still getting symptoms, your GP or asthma nurse may refer you to a specialist asthma clinic. It may take some time before you get an appointment, so you’ll still have to manage your condition through your GP until then. 

At the clinic they will try to work out what’s going on by answering these questions:

  • Is the type of asthma you have difficult to control asthma?
  • Is the type of asthma you have severe asthma?
  • Is there another reason why you’re getting your asthma symptoms?

You might have had tests to diagnose and monitor your asthma already, but to confirm or rule out a diagnosis of severe asthma you may need some extra tests.

You probably won’t need all these tests, though. Your asthma specialist will explain which ones you need and why.

“Everyone with asthma is different so the tests you’ll need will depend on your individual asthma symptoms, medical history, family history and any other conditions you have,” says Asthma UK’s in-house GP Dr Andy Whittamore.

“And because your asthma symptoms can vary over time, you may need to have these tests more than once to help your asthma specialist make the right diagnosis.”

Blood tests

Most people who see an asthma specialist are sent for blood tests.

Asthma specialists use these tests to:

  • rule out other causes of your symptoms (such as low levels of vitamin D)
  • look for signs of allergic inflammation in your blood
  • check if you have raised levels of eosinophil cells in your blood associated with eosinophilic asthma
  • see whether certain organs, such as your liver and kidneys, are working properly

“The results may show that you don’t have severe asthma and that your symptoms are caused by something else, such as anaemia (low levels of iron) or an infection,” says Dr Andy Whittamore.

“They may also give clues about how to manage your asthma. If you have high levels of cells called eosinophils, this shows you have a high level of allergic inflammation, so you may find targeted new treatments called monoclonal antibodies will help.

“And knowing that organs such as your liver and kidneys are functioning properly means that it’s possible to prescribe certain treatments that can’t be used if they’re not working well.”

Sputum induction test

This painless test involves collecting a fresh sample of sputum (a mixture of saliva and mucus) from your lungs so it can be analysed in a laboratory.

You will be asked to breathe in different concentrations of slightly salty water through a nebuliser and then cough them up to produce a sample.

You may be asked to do this test if your asthma specialist is trying to work out why you have underlying inflammation in your airways.

Checking the number of eosinophils (a type of white blood cell associated with eosinophilic asthma) in your sputum will help your asthma specialist see what’s causing the underlying inflammation and what treatments might help it.

24-hour pH monitoring and manometry tests

Both of these tests check for signs of gastro-oesophageal reflux disease (GORD), also known as acid reflux. This is when acid leaks out of your stomach and up into your oesophagus (the tube that takes food to the stomach) causing heartburn or indigestion. Heartburn is an uncomfortable burning sensation in your chest. Indigestion is a pain or discomfort in the stomach and/or under the ribs. 

24-hour pH monitoring involves passing a thin tube containing a sensor up your nose and down your throat to measure the acidity level (pH) in your throat over a 24-hour period. This tube is usually 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 tests help your asthma specialist work out how well the ring of muscle at the end of your oesophagus is working by measuring the pressure in your oesophagus. It involves passing a small tube containing pressure sensors up your nose and down into your oesophagus. 

Stomach acid irritates your airways and causes inflammation, which can make your asthma worse, so if your asthma specialist thinks you may have GORD − even if you’re not getting the typical GORD symptoms such as heartburn or indigestion − they may want to do these tests. 

“The results will help your asthma specialist to rule out or confirm that GORD is a cause of your asthma symptoms or making your asthma worse,” says Dr Andy. 

Chest X-ray

A chest X-ray is a quick and painless procedure, usually done in a hospital by a radiographer, that produces images of the inside of your chest.

Chest X-rays are commonly used to check that there isn’t anything else causing your asthma symptoms.

The results will help to make sure that your symptoms aren’t being caused by:

  • an infection such as pneumonia
  • a blockage in one of the airways
  • an enlarged heart
  • heart failure
  • pulmonary fibrosis (scarring of the lungs)
  • in rare instances, a tumour.

Remember that having this test doesn’t mean your specialist thinks you have lung cancer, it’s just a way of ruling it out.

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. 

This test is carried out in a hospital. The ring-shaped scanner rotates around your chest in small sections. Some clinics will also perform a CT scan of your nose and sinuses, as they can play a big role in the symptoms of some people with asthma.

The scanner doesn’t surround your whole body at once, so it’s unlikely you’ll feel claustrophobic.

A CT scan of your chest is increasingly used alongside a chest X-ray to check that there’s nothing else causing your symptoms.

“A CT scan of your chest allows your asthma specialist to carry out a more complete assessment of your lungs than an X-ray alone, and may help them look for and exclude other conditions such as bronchiectasis (a long-term condition where your airways become abnormally widened, leading to a build-up of excess mucus), diseases that affect the tissues that support your airways, and clots in your lungs,” says Dr Andy.


ECG stands for electrocardiogram. This 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 when your asthma specialist wants to see whether your heart is the cause of your severe asthma symptoms. Your asthma specialist will consider your age, medical history and symptoms to decide whether you need this test.

“The results of an ECG show your asthma specialist whether your heart is healthy enough to prescribe certain medicines, and 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,” says Dr Andy.


A 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.

The procedure is usually performed in an outpatient clinic so you won’t have to stay in hospital overnight.

This test is used when your asthma specialist wants to see inside your airways or needs to take a small sample of phlegm or tissue for examination. 

 “There are less invasive options available, such as a CT scan, so it’s used less often these days,” says Dr Andy. “If you need one, your asthma specialist will explain why.”

The results will help your asthma specialist rule out other causes of your asthma symptoms. It can also help pin down the specific pattern of your asthma if other tests haven’t given enough information.


This test uses a thin microscope to allow your asthma specialist to see what’s going on in your nasal passages. It’s usually performed in an outpatient clinic.

“A nasendoscopy can help to detect problems in your nose, sinuses and even your throat that can lead to chest symptoms and so make your asthma symptoms worse,” says Dr Andy. “This test is usually only done if your asthma specialist thinks your nose and sinuses may be triggering some of your symptoms.”

Because conditions that affect your sinuses 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.

Hyperventilation questionnaire

The hyperventilation questionnaire most often used by the NHS is the ‘Nijmegen Questionnaire’, which asks you how often you have had 16 different symptoms such as faster or deeper breathing, dizzy spells, blurred vision and palpitations, and gives you points for each one.

If your asthma specialist suspects you may be breathing too fast they may do this test. “Hyperventilating can sometimes make the symptoms of asthma worse,” says Dr Andy. “This is why it’s important to spot and treat this problem to help control your asthma symptoms.”

A score of over 23 out of 64 suggests you may be hyperventilating.  

According to the latest guidelines health professionals use on the management of asthma (BTS/SIGN), people who hyperventilate may benefit from physiotherapist-supervised breathing techniques such as the Papworth method and Buteyko Breathing Technique. 

These can improve your asthma symptoms and quality of life. In adults they can also reduce the amount of asthma medicines you need, although they don’t have an effect on lung function or inflammation.

Symptom and quality of life scores

These tests involve filling out questionnaires to find out what symptoms you’re experiencing and the different ways asthma may be affecting your life. 

In an Asthma UK survey, 91% of people said their severe asthma had an impact on everyday things, such as their ability to exercise, their family and social life, their work or school life and their holidays. In the same survey 82% of people said they’d experienced sleep loss and 66% had gained weight.

“If your asthma symptoms mean you can’t do things you used to be able to do, such as exercise or play with your children, these scores will help your asthma specialist find out how asthma is affecting your life,” says Dr Andy. “They’re also a useful way to monitor how well your asthma treatments are working.”

Asthma specialists use these tests to:

  • give them a clearer picture of your asthma symptoms
  • show them how asthma may be limiting your activities
  • reveal how you’re coping with the challenges of having frequent asthma symptoms
  • work out your response to longer-term treatment trials.

Depression and anxiety scores

These questionnaires are used to find out how having severe asthma is affecting you emotionally. In an Asthma UK survey, 68% of people with severe asthma said they’d had anxiety and 52% of people with severe asthma said they felt depressed.

“Because asthma symptoms that affect your quality of life can be worrying and get you down, it’s important for your healthcare team to understand how you’re feeling,” says Dr Andy.

“If you’re seeing an asthma specialist to diagnose or rule out severe asthma, they will usually consider screening you for anxiety and depression – often using these questionnaires. For some people with asthma, treating the depression and anxiety can have a big impact on your symptoms and how they affect you.”

“Evidence shows that people with low mood or anxiety can find it harder to control their asthma symptoms,” says Dr Andy. “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.”


Last updated March 2020

Next review due March 2022

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