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Home / Asthma / How to diagnose asthma

How to diagnose asthma

Learn about the different tests that diagnose asthma and if your symptoms are well-managed

Asthma is a common respiratory condition that affects your breathing. It is caused by inflammation of the airways and can result in wheezing, coughing and breathing difficulties.

As well as recognising symptoms, several tests can deliver a diagnosis. The main three tests for asthma are:

  • peak flow test
  • spirometry test
  • FeNO test

For those already managing asthma, you can also test to see how well-controlled your condition is. This is called an asthma control test (ACT).

To learn about the symptoms of asthma as well as these different tests, please continue reading.

What are the symptoms of asthma?

The signs and symptoms of asthma vary from person to person, but can look like any of the following:

  • wheezing (a whistling sound when you breathe)
  • coughing
  • shortness of breath
  • tightness in your chest
  • difficulty sleeping due to any of the above
A woman struggling to catch her breath

Many different factors or conditions can cause these symptoms. However, they are more likely to be caused by asthma if they:

  • occur repeatedly and frequently
  • are not accompanied by other symptoms of feeling unwell (e.g a fever or sore throat)
  • are worse at night or in the early morning
  • worsen (known as a ‘flare up’) during exercise
  • worsen when you are around allergens, such as pollen (which causes hay fever) and dust

Asthma can develop at any point in one’s life. If you have been experiencing any of the above symptoms, it’s best to get tested so you can receive a diagnosis.

How can I test for asthma?

If you want to take an asthma test, book an appointment with your doctor. They can then perform one or more of the following procedures.

Peak flow test

A peak flow test is the most basic type of asthma test. It measures how quickly you can blow air out of your lungs.

You perform this test by blowing into a handheld device called a peak flow meter. These are available at most pharmacies, which means you can also perform the test at home.

Close-up of a man blowing into a peak flow meter.

Instructions for using a peak flow meter are as follows:

  1. Set the dial to 0 on the device.
  2. Either standing or sitting, breathe in a full, deep breath.
  3. Put your lips to the mouthpiece and breathe out a single, forceful breath.
  4. Read the meter to find out your score and repeat the test if necessary.

If you can’t exhale air quickly enough, this may indicate that your airways are narrowed and that you need to start taking asthma medicine.

Spirometry test

Another type of asthma test involves using a spirometer. This is a small machine that is attached to a mouthpiece via a cable.

As well as asthma, it can be used to diagnose other lung conditions including:

  • COPD (chronic obstructive pulmonary disease)
  • cystic fibrosis
  • pulmonary fibrosis

A spirometry test works similarly to a peak flow test. It measures how much air you can exhale in one forced breath.

A man performing a spirometry test for asthma.

A spirometry test will look like the following:

  1. A clip will be placed onto your nose so that when you exhale, none of the air leaves your nostrils.
  2. Take a few practice breaths. Breathe deeply into your lungs and then exhale forcefully.
  3. Repeat these steps but with the machine. After inhaling, place your lips around the mouthpiece and exhale quickly, so that all the air escapes your lungs.

Spirometry test results don’t usually come back immediately. A doctor or specialist will analyse your results before deciding on your diagnosis.

FeNO test

A FeNO test (fractional exhaled nitric oxide test) detects asthma based on how much nitric oxide you exhale.

Exhaling too little nitric oxide can indicate a certain level of inflammation in the lungs. As a result, the patient may benefit from asthma medication.

A FeNo test is easy to do and completed with a small hand-held device.

  1. Sit comfortably or stand, whichever you prefer.
  2. Inhale deeply so that your lungs reach their full capacity.
  3. Place your lips around the mouthpiece and exhale gently for approximately 10 seconds.

Your results will show up on the screen of the device straight away.

An infographic about preparing for a FeNO asthma test

Please note: Avoid eating any foods containing nitrates (such as leafy greens and vegetables) for at least 3 hours before a FeNO test to ensure a reliable reading.

How severe is my asthma?

People with asthma may find that their symptoms worsen from time to time. This is normal and usually happens due to certain triggers like pollen, mould, humidity or exercise.

However, if your symptoms don’t return to normal after a flare-up, this can indicate that your asthma is worsening or becoming more severe.

If this applies to you, it’s important to visit a GP or asthma nurse. You’ll need to get the correct treatment to avoid severe symptoms and prevent asthma attacks.

Is my asthma well-managed?

In general, your asthma is well controlled if:

  • you use your blue reliever inhaler less than 3 times per week
  • you don’t wake up at night due to coughing or shortness of breath
  • you can take part in daily activities (including exercise) without many asthma symptoms

If one or more of these points doesn’t apply to you, you should visit a healthcare professional. Based on your symptoms, they may adjust your treatment so that you feel more in control of your asthma.

Asthma control test

If you’ve noticed changes in your condition, you can also perform an Asthma Control Test (ACT).

This test asks you several questions about how your asthma has affected you within the past four weeks.

It will ask about your sleep quality, any disturbances at work, how often you use your reliever inhaler, and if you feel in control of your breathing.

If the test tells you that your symptoms aren’t being well-managed, your doctor may need to make changes to your asthma treatment.

When should I see a doctor?

Overall, you should visit your doctor or a healthcare professional if:

  • you’re experiencing signs of asthma for the first time, and have never been diagnosed
  • you want to take an asthma test to receive a diagnosis
  • you think you may have another lung-related condition, such as COPD
  • your asthma symptoms have been harder to manage
  • you are worried that your asthma is becoming severe
  • you frequently wake up at night due to your asthma

Want to learn more about asthma?

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Medically reviewed by Dr. Caroline Fontana Written by our editorial team Last reviewed 14-02-2024

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Further reading

What to do during an asthma attack

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