Asthma can be difficult to diagnose in young children because many other conditions can cause similar symptoms.
Most children develop the symptoms of asthma by the time they reach school age. Some children also have other allergic (atopic) conditions such as eczema and hay fever.
There is no simple test to diagnose asthma, but certain combinations of symptoms and signs make it likely that your child has asthma.
Your GP will ask about your child's symptoms and listen to their chest. They will want to know when and how often your child has symptoms and if you have noticed anything that might trigger them. The GP will also ask about your child's medical history and whether there is a history of allergic conditions in your family.
If your GP suspects your child may have asthma, a number of tests can be carried out to confirm the diagnosis.
Sometimes, children may be given an asthma inhaler as a trial treatment. If this helps their symptoms, the child probably has asthma. However, asthma medicines can be relatively ineffective in infants and young children, so a negative response may not definitely rule out asthma.
Spirometry
To assess how well your child’s lungs work, a breathing test called spirometry is carried out. At the GP surgery, this test can only be done reliably in children over the age of five.
Your child will be asked to breathe into a machine called a spirometer. The spirometer takes two measurements: the volume of air that your child can breathe out in one second (called the forced expiratory volume in one second or FEV1) and the total amount of air that your child can breathe out (called the forced vital capacity or FVC).
Your child may be asked to do the test a few times to get a consistent reading.
The readings are compared with normal measurements for children of your child’s age. This will show if your child’s airways are obstructed.
Sometimes, an initial set of measurements is taken, and then your child is given a medicine to open up the airways (a reliever inhaler). Another reading is then taken. If the reading is much higher after taking the medicine, this suggests your child has asthma.
Peak expiratory flow rate test
A small hand-held device, known as a peak flow meter, can also be used to measure whether the lung airways are narrowed. The peak flow meter measures the highest flow of air that we can blow out of our lungs during one breath. This is called the peak expiratory flow rate (PEFR).
You may be given a peak flow meter to take home and a diary to record measurements of your child’s peak flow. Your child’s diary will also have a space for you or your child to record their symptoms. This will help you recognise when your child’s asthma is getting worse.
The PEFR test is only suitable for children who are over five years of age.
Other tests
Some children may need more tests. The additional tests may confirm the diagnosis of asthma or may help diagnose a different condition that causes symptoms similar to those of asthma. The results of these tests will help you and your doctor plan your child’s treatment.
Airway responsiveness tests
This test is used to see how the airways react when they are stimulated. The most common test of this type in children is an exercise test. Your child will blow into a peak flow meter or a spirometer and then be asked to run as hard as they can for a few minutes. After the run, the breathing tests will be repeated. A significant decrease in the measurements may indicate your child has asthma.
Tests of airway inflammation
These tests are normally done in a hospital asthma clinic.
- Phlegm sample - the doctor may take a sample of phlegm to check whether there is inflammation in the lungs.
- Nitric oxide concentration - as your child breathes out, the level of nitric oxide in the breath is measured. A high level of nitric oxide can be a sign of airway inflammation.
Tests of allergy
Skin testing or a blood test can sometimes help establish whether your child’s asthma is associated with specific allergies, such as allergies to dust mites, pollen and foods.
