Asthma – Diagnosis

ASTHMA DIAGNOSIS

The effective treatment of asthma depends on correct diagnosis. The joint guidance from the British Thoracic Society (BTS), NICE and the Scottish Intercollegiate Guidelines Network (SIGN), emphasises the importance of objective tests to support a diagnosis in people with suspected asthma, or to confirm the diagnosis in people who are not responding to therapy.¹

General practice nurses (GPNs) who have the relevant training and competencies are often involved in diagnosing people who present with respiratory symptoms and a clear understanding of how the diagnosis is made is therefore essential. In people who already have a diagnosis of asthma, it is worth reviewing the diagnosis if they are poorly controlled despite asthma treatment – so in essence anyone involved in the care of people with asthma should be aware of how the diagnosis is reached.

NICE recommends obtaining a structured clinical history in people with suspected asthma, specifically checking for:

• Reported wheeze, noisy breathing, cough, breathlessness or chest tightness; any variation (worse during the night or early morning, or seasonal)
• Any triggers that make symptoms worse
• A personal or family history of asthma or allergic rhinitis
• Symptoms that suggest an alternative diagnosis

Diagnosis of asthma should only be confirmed with a suggestive history, supported by an objective test. Record as 'suspected asthma' until objective tests have been performed.

The preferred sequence for objective tests in adults (people aged over 16 years) is: 

• Measure blood eosinophil count or fractional exhaled nitric oxide (FeNO). Diagnose asthma if the eosinophil count is above the laboratory reference range or FeNO level is 50 parts per billion (ppb).
• If asthma is not confirmed, measure bronchodilator reversibility (BDR) with spirometry. Diagnose asthma if the FEV1 increase is 12% or more and 200 ml or more from the pre-bronchodilator measurement, or if FEV1 is 10% or more of the predicted normal FEV1.
• If spirometry is not available or is delayed measure peak expiratory flow (PEF) twice daily for 2 weeks. Diagnose asthma if PEF variability is 20% or more.
• If none of the above tests confirm asthma, but asthma is still suspected on clinical grounds, consider referral for a bronchial challenge test. Diagnose asthma if bronchial hyper-responsiveness is present.

In children aged 5 to 16 with a history suggestive of asthma:

• Measure FeNO level. Diagnose asthma if the FeNO level is 35 ppb
• If FeNO level is not raised, or FeNO testing is not available, measure BDR with spirometry. Diagnose asthma if the FEV1 increase is 12% or more and 200 ml or more from the pre-bronchodilator measurement, or if FEV1 is 10% or more of the predicted normal FEV1.
• If spirometry is not available or is delayed measure PEF twice daily for 2 weeks. Diagnose asthma if PEF variability is 20% or more.
• If none of the above tests confirm asthma, but asthma is still suspected on clinical grounds, either perform skin prick testing or measure total IgE level and blood eosinophil count. Diagnose asthma if there is evidence of sensitisation or a raised total IgE level and the eosinophil count is more than 0.5 x10⁹ per litre.

In children under 5, diagnosis of asthma is difficult because it is difficult to do the tests and there are no good reference standards. For children under 5 with suspected asthma, treat with inhaled corticosteroids and review regularly. Attempt objective tests when they are aged 5, and repeat as necessary every 6 to 12 months until satisfactory results are obtained. Refer for specialist assessment if the child's asthma is not responding to treatment.

References

1. BTS/NICE/SIGN NG245. Asthma: diagnosis, monitoring and chronic asthma management; 27 November 2024. https://www.nice.org.uk/guidance/ng245