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Asthma Diagnosis

Before treatment can begin, our doctors need to be sure that asthma is the cause of your symptoms.

Problems such as coughing and wheezing can occur for a variety of reasons, so it's important that a correct diagnosis is made.

This will ensure you get the most effective treatment straight away. If you're worried about your symptoms, you can get an appointment with an experienced GP in minutes and receive a diagnosis.

How Our Doctors Diagnose Your Asthma

During your online appointment, the doctor will ask you lots of questions about your symptoms in order to see if asthma could be the cause, such as:

  • Do you have any of the common symptoms of asthma, such as shortness of breath, coughing, wheezing and chest tightness?
  • Have you identified any possible triggers?
  • Do your symptoms occur at certain times of day?
  • Do you have a medical history of breathing problems?
  • Do you have any allergies?

If you’re suffering from symptoms such as coughing or wheezing, this will be noticeable in your face-to-face consultation.

Along with your answers to these questions, this will sometimes be enough for a doctor to diagnose you with asthma.

Alternatively, they might decide to confirm or rule out asthma by providing you with a blue reliever inhaler to see if that helps your symptoms.

Woman with asthma takes deep breath

Asthma tests

If our doctors need more information to make a firm diagnosis, they can refer you for further tests. Here are some of the most common tests for asthma:

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Checking Your Airways

Asthma occurs when your airways become so narrowed or blocked that it becomes difficult to breathe normally.

These tests will investigate why you’re having problems with your airways and help the doctor decide how to proceed with your asthma treatment.

Responsiveness test

This test measures how your airways respond to potential asthma triggers. You’ll breathe in a substance and take a spirometry test to see if your symptoms have worsened. The results will help your doctor decide if you have asthma and, if you do, which treatments will work best.

Because this test could potentially cause asthma symptoms, it’s usually carried out in a hospital under supervision. Our doctors can provide a referral for this test.

FeNO test

FeNO stands for ‘fractional exhaled nitric oxide’. Essentially, you’ll breathe into a machine that will measure how much nitric oxide there is in your breath. The amount is important, as your body produces a higher volume of nitric oxide when you’ve breathed in something you’re allergic to.

It’s still possible to have asthma even if your FeNO reading is low, but the results will help your doctor choose your medication and create your action plan. You may also need to provide a mucus sample to test alongside your FeNO results.

Man with bike on a hill

Breathing and Lung Capacity

These lung function tests compare your breathing with the expected results for someone of your age, gender, height and lifestyle. They’re very quick and safe.


Spirometry tests the amount of air you can hold in your lungs and the amount of air you produce when you breathe out.

You’ll breathe out as hard and fast as you can through a device called a spirometer. You may need to repeat the test a couple of times in order to make sure the results are accurate.

If your lungs are able to hold a normal amount air, but you breathe out a lower than usual amount, this could indicate you have asthma.

Some patients undergo a second test, where they’re given medication known as a bronchodilator that causes the airways to widen, before breathing into the spirometer a second time.

If your results are much better the second time around, this could indicate that you have asthma.

Peak Flow

The peak flow test measures how long it takes you to get all the air out of your lungs in one breath. You’ll take a deep breath and breathe out as hard as you can into a peak flow meter.

If you have an idea of what your trigger is, you can take a peak flow meter home with you, so that you can measure your breathing at different times of the day.

This will help to establish a pattern of when your airways are most affected by asthma symptoms and potentially confirm what your triggers are. Your doctor can use this information to help with your action plan.

Woman breathing freely

Testing for Allergies

There are many allergies that can cause symptoms similar to asthma. If your doctor wants to check whether certain triggers cause an allergic reaction, these tests can provide valuable information.

Skin test

The most common allergy test, which can provide results in as little as 15-20 minutes. Your skin is pricked with a small amount of a potential trigger. If a rash or blister forms, you’re allergic to that substance.

Blood test

A sample of your blood is taken to test how many antibodies your immune system produces in response to a potential asthma trigger.

Woman in a meadow

Diagnosing Asthma in Children

Diagnosing asthma is much more complicated for children than it is for adults. There are a number of reasons for this.

If your child is aged under five, their lungs aren’t developed enough to gain any meaningful results from a spirometry or peak flow test.

As these tests aren’t as reliable at this stage, younger children are often diagnosed with ‘suspected asthma’. This means the doctor thinks it’s a possibility, but will need to observe your child over a longer period to make a full diagnosis.

They may suggest a trial treatment, where your child uses a certain medicine for 2-3 months to see if it has an effect on your child’s symptoms.

If your child responds well, it’s likely that they do have asthma. Your doctor can then use the results from the trial treatment to work out the lowest effective dose needed when full treatment starts.

Diagnosing asthma in children

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