In accordance with the motto of this year’s World Asthma Day, “Uncovering Asthma Misconceptions”, this is the fifth post of our mini-series about asthma based on our patient booklet “Fast Facts for Patients and their Supporters: Asthma”. Here, we focus on the tests your doctor will run if your symptoms suggest asthma.
Spirometry is a simple non-invasive test that measures how hard and how much you can breathe out (exhale). Sometimes how hard you can breathe in (inhale) is also measured in the same test. It is usually performed before and after you have inhaled reliever medication to see what difference the medication makes.
It is difficult to do spirometry on children under 5 years old. In very young children, it is best performed in a clinic that specializes in testing children.
You may hear your doctor talk about FEV1 or FVC. These are measurements that the doctor makes from your spirometry test.
FEV1 (forced expiratory volume in 1 second) is the maximum amount of air you can blow out in 1 second. People with asthma often (but not always) have a lower-than-normal FEV1. Your FEV1 should increase after a dose of reliever medication.
FVC (forced vital capacity) is the total volume you can blow out after taking the deepest breath possible. People with asthma usually have a normal FVC. If your FVC is lower than normal, you may have a different lung disease.
One of the easiest ways to measure the force of blowing is with a peak flow meter. This is a cheap, portable, handheld device that is very easy to use. Peak flow meters are available at pharmacies and online. Peak flow can be used to diagnose asthma and to monitor your asthma after diagnosis.
Peak flow measurements reflect what is happening in your airways. Keep a daily record of your peak flow, morning and night. If your asthma is poorly controlled, your peak flow will be up and down.
The bronchial challenge test (or airway hyperresponsiveness test) assesses how your airways respond to an asthma trigger. It is used only if other tests, including spirometry, do not clearly show that you have asthma. It is not recommended for children.
The test is carried out in hospital by trained staff who are on hand to reassure you if your breathing worsens. You will be asked to inhale an irritating substance (for example, a saltwater mist) through a handheld device or nebulizer. Your response will be monitored and, if necessary, treated.
FeNO (fraction of expired nitric oxide) is another ‘blowing’ test that measures how much nitric oxide is being produced in your airways. The level of nitric oxide can help show what is causing the inflammation in your airways.
FOT (forced oscillation technique) measures air pressure and flow in your airways. You will be asked to breathe normally in and out through a mouthpiece attached to a machine. FOT can be used on people who are unable to do spirometry, such as very small children, but other tests are usually needed to get a definite asthma diagnosis. Research is under way to see if this test can be used to diagnose asthma in very young children (under 3 years old).
X-Rays and Other Imaging
The features of asthma do not show up well on chest X-rays or other types of chest scans. However, scans do provide a picture of the lungs and can show if something other than asthma is going on, for example heart failure, emphysema or lung infection.
Skin prick tests can be carried out to find out if you have an allergy and what you are allergic to.
Drops of liquid containing small amounts of allergens (for example, animal fur, pollens, house dust mites, molds) are placed on your forearm. A small sterilized needle is then pressed into the skin to break the surface.
If an itchy weal appears that is larger than the positive control weal made by histamine, then you are allergic to that substance. The bigger the skin reaction, the more severe the allergy. You may respond to several substances.
It is also possible to test your blood for allergens, but the skin test can test for more allergens in one go.
Could My Breathing Difficulties Be Something Else?
Many illnesses can mimic asthma. Other illnesses that can cause breathing problems include chronic obstructive pulmonary disease, abnormal function of the vocal cords and wheezing after a viral infection. Your doctor will make sure it is asthma that you have and not something else. Talk to your doctor if you have any worries about your asthma diagnosis.
Please check out the previous and the next post of our series here:
Information based on Fast Facts for Patients and their Supporters: Asthma (Karger, 2020).