Which tests for asthma are there?
GPs use a variety of tests to diagnose if you have asthma. These tests examine things such as how well your lungs are working, whether your lungs’ airways are narrowed or inflamed, and if you have any allergies that might be triggering the symptoms of asthma.
Peak flow test
This test, also known as a peak expiratory flow test or PEF, is a lung function test which measures the strength of your out breath. It shows the doctor how open your airways are and how well your lungs are working. If you are diagnosed with asthma it also helps you to monitor your condition at home.
The test uses a plastic device called a peak flow meter, which you blow into as hard and fast as you can. The device takes a measurement of the force of your breath using a scale on the side and this measurement is called your ‘peak flow’.
Peak flow scores vary according to the age, height and sex of each patient. Peak flow tests can be done at any time of the day, and variations in the readings can help you and your doctor to see when your asthma is worse, sometimes before you even realise it, so that you can use your medication and/or seek medical help before symptoms deteriorate.
Readings from peak flow tests can help your doctor to diagnose if you have asthma and recommend the best course of treatment.
Spirometry (also known as the reversibility test) is another common lung function test used in the diagnosis of asthma. As with the peak flow test, it measures how well your lungs are working and whether your airways are restricted in any way.
A spirometer is a device that measures how well you breathe in and out. The device has a mouthpiece that you blow into. During the spirometry test the doctor or asthma nurse asks you to take a deep breath, then place your lips around the mouthpiece and breathe out as fast and long as you can until your lungs are empty of air. You might also be asked to breathe in deeply then breathe out slowly into the mouthpiece as long as you can. You will need to do the test a number of times so that your nurse or doctor can get an accurate reading of your lung function.
Once the reading has been taken, you will be asked to inhale a reliever medication, a medicine that relieves the symptoms of asthma and opens up the airways. When this has been given around 20 minutes to take effect, you will be asked to breathe into the spirometer again so that further readings can be taken and it can be seen if your lung function has improved as a result of taking the reliever medication.
The spirometer results show how well you can breathe out compared to normal measurements for your age, height, weight and gender. If your readings improve after taking the reliever medication, it’s likely that you do have asthma.
A FeNO (fractional exhaled nitric oxide) test measures your nitric oxide levels when you breathe out, using a hand-held device. This test is used in the diagnosis of asthma because nitric oxide is produced in your lungs when your airways are inflamed due to being allergic to something. High levels of nitric oxide in your out breath can be an indication of inflamed airways, which means that you have asthma.
In people already diagnosed with asthma, the FeNO test is often used in conjunction with a spirometry test to identify if you have allergic or non-allergic asthma. This helps to inform which treatment is best for controlling your asthma.
If your doctor thinks that you have allergic asthma (when your symptoms are triggered by allergens such as pollen or animal fur) then they may give you an allergy test.
A blood test or a skin-prick test may be carried out to determine what you are allergic to and if this triggers asthma symptoms. These can be carried out by your GP or you might be referred to a specialist doctor in hospital.
Blood tests for allergies show if certain antibodies have been produced in your blood after exposure to a specific allergen. The skin-prick test involves pricking the skin with a tiny needle which applies a small amount of a suspected allergen to the skin. The test shows that you are allergic to the allergen if the skin reacts by becoming swollen, itchy and red.
If the tests show that you are allergic to a specific substance then your doctor or asthma nurse will recommend that you avoid it if possible. If it isn’t possible to avoid it and it’s likely to trigger your asthma symptoms, they will advise you on ways to manage the situation.
Airways responsiveness test
If your doctor or asthma nurse concludes that initial test results didn’t give a definitive diagnosis of asthma, then you may be referred to an asthma specialist for further tests.
The airways responsiveness test is a more advanced test for asthma which is carried out in hospital by an asthma specialist. It looks at how the airways in your lungs react when exposed to certain irritants known to trigger asthma symptoms.
If you don’t have any reaction to the triggers, then it is unlikely that you have asthma. If your airways become inflamed and narrowed when you breathe in these substances, then it is likely that you do have asthma. The asthma specialist can then devise an asthma treatment plan for you.