How is severe asthma diagnosed?

Find out how severe asthma is diagnosed and what tests you’ll need to confirm your diagnosis

What are the signs of severe asthma?

Your GP may decide to refer you for further assessment and tests if any of the following apply to you:

  • you’re on long-term steroids for your asthma 
  • you’re waking up at night because of your asthma  
  • you’re using your reliever inhaler three or more times a week 
  • your asthma is affecting your everyday life or activity levels 
  • you’ve had two or more asthma attacks needing oral steroids in a year 
  • you’ve had one or more asthma attacks needing treatment in hospital in a year 
  • you’re finding your asthma symptoms hard to control, even with prescribed treatments.

Find out how to get a referral for specialist care.  

'Difficult' or severe asthma?

Only around 4 in 100 people with asthma are diagnosed with severe asthma. This is a type of asthma that’s difficult to control even if you’re following your treatment plan and using your medicines in the best way. 

Even if your asthma is described as ‘difficult’ and you’re having lots of asthma attacks, it doesn’t always mean you have severe asthma.  

Although both severe asthma and ‘difficult’ asthma are hard to control, most people with ‘difficult’ asthma notice improvements with good support from their GP. Find out more about ‘difficult’ asthma.  

If your asthma continues to be uncontrolled, even though you’ve had support from your GP to manage your difficult symptoms, you may need a referral to specialist care. 

Why it’s important to get a referral

It’s important to get a referral so that you can:

  • access a range of different respiratory specialists 
  • be assessed for the best treatments for your type of asthma 
  • get a diagnosis and find out more about the type of asthma you have 
  • avoid taking high doses of steroid tablets long-term.  These are life-saving treatments, but they can have side effects if taken long term. 

Use our severe asthma tool to find out if you’d benefit from newer, better treatments for severe asthma. You can also read our report: Do No Harm, safer and better treatment options for people with asthma

Getting a diagnosis of severe asthma

To get a diagnosis of severe asthma you’ll need to work closely with your specialist team to review your asthma. This is so you can:

  • understand your triggers at work or at home 
  • understand how your asthma affects you and those close to you 
  • talk about how you’re feeling, especially if you feel anxious or depressed 
  • talk about other health conditions or allergies that could be making your symptoms worse. 

It can take time to diagnose severe asthma. There are different types of severe asthma (phenotypes).  This includes eosinophilic severe asthma, where severe symptoms are triggered by higher levels of cells called eosinophils.  
Your specialist team can offer you tests to confirm your diagnosis and find out which type of severe asthma you have.  Once it’s clear what type of severe asthma you have, your specialists can work out the best treatments for you.  You may be eligible for specialist biologic treatments.   

Tests for severe asthma

If your doctor thinks you could have severe asthma, you’ll need tests to confirm it. Tests will help you and your specialist team find out if you have: 

  • severe asthma  
  • allergic severe asthma 
  • non-allergic severe asthma
  • other conditions that are causing your symptoms or stopping you from managing your asthma well. 

A bronchial challenge test will find out how sensitive your airways are. It is sometimes called a provocation test or a direct challenge test. Read more about having a bronchial challenge test.

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 specialist rule out other conditions that could be making your asthma symptoms worse. Read more about having a bronchoscopy

An electrocardiogram (ECG) is a simple test that is used to check your heart’s rhythm and electrical activity.  An ECG checks whether your heart is healthy enough to take certain medicines. It can also show other possible causes of your asthma symptoms, such as an irregular heartbeat, an enlarged heart, or previous damage to your heart muscles. 

Read more about having an ECG.

A FeNO (fractional exhaled nitric oxide) test measures how much nitric oxide is in your breath. It is most often used to diagnose asthma.  It could also be used in a specialist centre to monitor your severe eosinophilic asthma. Read more about having a FeNO test.

This test measures the amount of oxygen that passes from your lungs into your blood.  This test can help monitor your condition. Read more about having a gas transfer test

You might need an imaging scan, like a CT scan or X-ray. These tests can give you a more complete picture of your lungs. 

Chest X-rays give an image of the inside of your chest.  A CT scan uses X-rays and computers to give a detailed 360-degree image of the inside of your lungs. Read more about imaging scans.

A lung volume test shows the total amount of air in your lungs . It is sometimes called lung plethysmography . It will let your specialist team know if your lung condition is obstructive or restrictive. Asthma is obstructive, which means the lungs never empty completely. 

Read more about having a lung volume test.

Peak flow is a lung function test that measures how fast you can breathe out. It is used to diagnose and monitor asthma. Read more about peak flow.

A spirometry test measures how much air you can breathe out in a set time.  It can help to diagnose asthma. 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. Read more about spirometry tests

In a sputum induction test, a sample of your mucus (sputum) is taken.  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. Read more about having a sputum induction test.

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

There may be some tests that you need to do more than once so that your specialist can make the right diagnosis. If you don’t like the idea of having lots of tests, remember they are there to help you manage your asthma better.

Get support

Call our Helpline for support with your condition. Get advice on your medicines, symptoms or travelling with a lung condition, or just call us to say hello.

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