How is it assessed?
Pulmonary Function Tests/Spirometry
Most diagnoses of asthma will be based on history of symptoms including -:
- Wheezing – musical sounds heard in the chest during asthma exacerbations
- Coughing – especially at night and in the morning
- Chest tightness
- Difficulty breathing or shortness of breath
Examination findings are likely to include evidence of wheezing on auscultation during exacerbations, wheezing may be absent between attacks.
Peak Flow Rate Monitoring (PEFR monitoring)
In children over 5 Peak Flow Rate (PEFR) Monitoring is likely to be done. A Peak Flow is measured using a Peak Flow Meter. This is a simple device which the child blows into as hard as possible, the device measures maximum ‘puff’ in litres per minute (L/min). The value can be compared to the normal value expected given the height of the child or the most recent personal best PEFR. PEFRs may be given as a ratio in medical evidence; a ratio of 1 is normal and could imply that the asthma is well controlled or that there is no asthma. Often PEFR will be measured and charted for some days or weeks to assess whether there is an asthmatic pattern and whether this improves with asthma treatment. Typical asthma patterns include variation in peak flow measurements – peak flow in people without asthma is relatively constant, variation of up to 5% is normal, variation of more than 15% indicates asthma. A typical pattern of variability is ‘diurnal variation’ – this means the peak flow measurement varies through the day, being typically lower in morning and is a hallmark of asthma. Another hallmark of asthma is ‘reversibility’. This means that a low peak flow can be significantly improved by using a beta-agonist inhaler. A person without asthma would only show minimal increase of peak flow after using one. The Peak Flow meter can be used at home to chart PEFR in severe asthma to enable treatment adjustments. It is likely to be used for a few weeks at a time in mild to moderate asthma.
In the majority of children with mild to moderate asthma PEFR monitoring and response to treatment will be the only investigations used.
In children who fail to respond to asthma treatment or who appear to have severe asthma requiring intensive treatment further investigations may be performed.
Pulmonary Function Tests/Spirometry
This test involves blowing into a spirometry machine which measures the following -:
- Forced Vital Capacity (FVC) – volume of air that can be breathed out.
- Forced Expiratory Volume in 1 second (FEV1) – volume of air that can be breathed out in 1 second.
The expected peak flow and spirometry readings for a child will vary depending on age and height. If an interpretation of the readings is not given in medical evidence but the readings are provided, seek medical advice for interpretation. In asthma the readings will show an ‘obstructive defect’ – this means the test shows that breathing out is restricted compared to normal and is characteristic of asthma. In a case of severe asthma, these readings would be expected to be abnormal with an FEV1 of less than 80% of normal, in-between asthma exacerbations.
Exercise testing
This involves the child exercising and then having peak flow monitoring or spirometry. Children with severe asthma are more likely to have a positive exercise test. Having a positive exercise test can mean that asthma is not well controlled on current treatment.
Allergy testing
Children with severe asthma that is hard to control are likely to have allergy testing to assess whether asthma is due to avoidable inhalant allergens. Very rarely, food allergy or food preservatives such as sulphites may worsen asthma control and avoiding foods to which the child is allergic on testing or that contain preservatives can improve asthma control.
Chest X-ray
These are generally normal in asthma but are used to rule out other causes of respiratory illness.
Tests for rhinitis
These include Computed Tomography (CT) scanning of nasal sinuses – treating allergic rhinitis (inflammation of the mucous membrane of the nose) in addition to asthma when it is present can significantly improve asthma control.
All these tests will clarify whether asthma is the condition causing breathing difficulties. Where asthma is confirmed, further testing will guide therapy. For example, allergy testing may reveal inhalant allergies which can be avoided to improve asthma control and enable treatment of allergic rhinitis, which can improve asthma control.
