A diagnosis of Asthma should be made wherever possible using evidence taken from an objective test, and the most widely available objective tests include Spirometry with reversibility, PEF diary and Fractional Exhaled Nitric Oxide (FeNO). The difficulty with these tests is that they are not all possible in all age groups.
- A single peak flow is inadequate to demonstrate reversible airways disease
- Clinic peak flow is useful to establish a child’s personal best peak flow and to check on technique
- Complete 2-4 week peak flow diary. This can be recorded on the NHS Asthmahub for parents app
- Evidence of 20% peak flow variability supports a diagnosis of asthma
- Once on treatment with ICS expect peak flow to increase and variability to reduce
Spirometry and bronchodilator reversibility testing
- For spirometry to be meaningful, the patient needs to be able to consistently exhale maximally to achieve “flow limitation”. Inadequate technique is common in children and can produce misleading results.
- Children aged > 12 years can perform spirometry reliably. Many children aged 5-12 years can do spirometry with practice and expert guidance.
- Children with asthma may have normal spirometry when well.
- Patients need to omit all inhaler treatments on the day of spirometry.
- A positive bronchodilator reversibility test in children is de ned as an increase in FEV1 of 12%, in response to bronchodilator therapy.
- FEV1/FVC ratio in children varies with age and may be as high as 0.90. Using an adult cut-off to diagnose obstructive airways disease of 0.70 may therefore miss some children with obstructive airways disease. Look for and use lower limit of normal (LLN) if available.
Skin prick tests, specific IgE tests, blood eosinophilia
- Positive skin-prick tests, aero- allergen specific IgE tests, and blood eosinophilia >4% increase the probability of asthma in school children
- However, these tests have limited value in making a diagnosis of asthma (the positive predictive value is low). They may be used to corroborate atopic status.
- Non-atopic wheezing is as frequent as atopic wheezing in school-aged children.
Fractional exhaled nitric oxide (FeNO)
- FeNO >35ppb is de ned as a positive result in children <16 years of age (who have not received steroid therapy)
- A positive FeNO is not diagnostic of asthma
- A negative FeNO does not exclude asthma
- FeNO in children < 12 years is harder to perform and interpret and should only be performed in specialist asthma clinics