Asthma Diagnosis

Reviewed by Dr Claudia Pastides, 17th April 2019

Diagnosing asthma

If you have suspected asthma, it’s important to receive the right treatment as soon as possible. Often, a doctor can diagnose asthma simply by asking a few questions about your symptoms, or testing an inhaler to see if it improves them. However, because asthma symptoms such as wheezing and coughing are signs of other conditions, you may need to undertake some further breathing tests for an accurate diagnosis.

There isn’t a single test which can diagnose asthma, so you may be asked to do a number of different tests so the doctor can confirm or rule out asthma. It can sometimes be difficult to diagnose asthma in children. Find out more about the tests you may be required to do with your GP.

Breathing tests

A spirometry test can be used to see how well your lungs and airways are working. It involves breathing hard and fast into a device called a spirometer. The measurements are compared to the average results of people who do not suffer from asthma. You will probably be asked to do this a few times, including after taking asthma medication to see whether the test results show an improvement.

You may also be asked to carry out a peak flow test. This measures how well you are able to breathe out. This kind of test can be repeated at different times of the day to record when symptoms are at their worst, so it can be taken home for ongoing measuring.

If the diagnosis remains in doubt then a specialist may perform further, more complex tests as explained below.

Allergy tests

If your doctor thinks your symptoms may be allergy related, they may perform some simple allergy tests to rule out asthma and find your allergen. The most common tests are skin prick tests and blood sample tests.

Airway and inflammation tests

Specialists may use an airway responsiveness test to see how you react to an asthma trigger. You will either be asked to breathe in medication which narrows the airways in the same way as a trigger, or exercise can also be used. A spirometry test is then performed to see how your breathing was affected.

It can also be useful to check the inflammation of your airways, which can be done using two methods. A mucus sample can be tested, or you may have to have the nitric oxide level in your breath tested. A machine can be used to read the level of nitric oxide, and a high level indicates inflammation.

These tests are useful to help doctors confirm you have asthma and decide which treatment plan is best for you.

The information provided is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Seek the advice of a doctor with any questions you may have regarding a medical condition. Never delay seeking or disregard professional medical advice because of something you have read here.