CPD: Key questions on asthma diagnosis and management

GP respiratory specialist Dr Fiona Mosgrove discusses current recommended practice in the diagnosis and management of asthma, including appropriate diagnostic steps, use of eosinophil counts, the principles of recommended treatment regimens and use of fractional exhaled nitric oxide (FeNO) in monitoring. Complete the full module on Pulse 365 today.

Learning objectives

This module will enhance your knowledge and bring you up to date on:

• Key updates within joint NICE/BTS/SIGN guidelines on asthma diagnosis and management.
• Recommended diagnostic pathways in children and adults, including stepwise approach to testing and the role of PEF measurement.
• When blood eosinophils should be tested in adults and how to interpret results.
• Appropriate initial management of newly diagnosed asthma, including the use of AIR therapy and MART, how to escalate treatment and the place of SABA monotherapy.
• When and how to switch existing patients to new treatment regimens.
• Assessment and management of acute exacerbations in primary care.
• Key components of an asthma self-management plan.

1. According to the most recent NICE guidance, what sequence of investigation should we use to diagnose asthma in both adults and children?

The new joint guidance from NICE, the British Thoracic Society (BTS) and Scottish Intercollegiate Guidelines Network (SIGN)¹ advises that clinical assessment remains vital to establish that the person has symptoms that suggest a diagnosis of asthma. If they do, then objective evidence of airway inflammation should be sought to confirm the diagnosis.

The guidance sets out a clear sequence of tests in adults and in children. Only one test needs to be positive to confirm a diagnosis of asthma. If a test is negative, then the next test in the sequence should be used. If all tests are negative and clinical suspicion remains high for a diagnosis of asthma then the patient should be referred to secondary care for further assessment. The sequence of tests and cut-off values in adults and children over 16 are laid out in the NICE algorithm (Figure 1) and summarised in table 1 below.

The recommended initial test is the fractional exhaled nitric oxide (FeNO) test, measuring nitric oxide in the exhaled breath – a biomarker of allergic inflammation in the airways. The test is relatively simple to perform, requiring less effort and taking less time to perform than spirometry. NICE advises that an alternative option in adults is to measure the eosinophil count, if FeNO is not available.

It is important to note that FeNO and blood eosinophil counts are both suppressed by oral and inhaled steroids. 

Table 1. Order and thresholds of diagnostic tests in adults and young people >16.

For diagnosis in children aged 5-16 years, the recommended sequence of tests and test thresholds are outlined in the NICE algorithm (Figure 2) and summarised in table 2 below.

Table 2. Order and thresholds of diagnostic tests in children aged 5-16 years.

2. Measuring eosinophils in adults as a means of diagnosing asthma is quite a change for GPs. What is the rationale behind this? A one-off reading also seems odd – would there not be some fluctuation meaning that a normal result might warrant repeating?

Eosinophils are key cells in the inflammatory cascade in asthma. They can drive the inflammatory process and are suppressed by inhaled and oral steroids. Some of the new biologic treatments for asthma block the activity of eosinophils and reduce exacerbation frequency.²

Eosinophils are known to be a risk factor for asthma exacerbations and patients with a high eosinophil count despite high doses of inhaled corticosteroid are particularly at risk.³ It has been accepted, for some time, in difficult and severe asthma clinics that eosinophils are often involved in the pathophysiology of asthma and targeting them can produce clinical improvement.

The guidelines committee looked at the evidence for eosinophils as a diagnostic test to support a diagnosis of asthma.¹ The available evidence in adults is generally of low or very low quality and the seven studies included in the committee’s review varied considerably in terms of the population demographics (such as smoking status and current use of inhaled steroids) and in the cut-off points used to define a high eosinophil count.  The committee noted that those studies that featured a high cut-off point for diagnosis of eosinophilia had a high specificity for asthma. This finding, combined with the easy availability and relative inexpense of performing a full blood count, resulted in inclusion of a blood eosinophil count above the upper limit of normal as a test confirming a diagnosis of asthma in a patient with a suspicious clinical history. 

If serial eosinophil counts are available, it is certainly worth looking at these. However, low results while on treatment with oral or inhaled steroids are certainly expected, so for patients already on treatment, eosinophil counts aren’t always helpful.

3. Why does latest guidance suggest we should consider measuring FeNO at an adult asthmatic’s regular review?

As above, FeNO is suppressed by inhaled and oral steroid treatments. It is a helpful tool to assess likely adherence to medication and response to escalations in dose of inhaled steroid. Patients with a persistently high FeNO count may not be taking their inhaled medications as prescribed or have poor inhaler technique, or severe airway inflammation that even high doses of inhaled corticosteroid are insufficient to suppress.

FeNO gives a number that clinicians can use as part of a discussion and education with the patient about airway inflammation, its link with asthma symptoms and the treatments that are effective in controlling it. It provides a useful metric to monitor tweaks in treatment that might improve disease control, and allows identification of patients with true severe asthma who will need further assessment.

Dr Fiona Mosgrove is a GPwSI in respiratory medicine in Aberdeen

References

1. NICE/BTS/SIGN. Asthma: diagnosis, monitoring and chronic asthma management (BTS, NICE, SIGN) [NG245] 2024
2. Kerkhof M, Tran T, Allehebi R et al. Asthma Phenotyping in Primary Care: Applying the International Severe Asthma Registry Eosinophil Phenotype Algorithm Across All Asthma Severities. J Allergy Clin Immunol Pract 2021;9(12):4353-70
3. Couillard S, Do W, Beasley R et al. Predicting the benefits of type-2 targeted anti-inflammatory treatment with the prototype Oxford Asthma Attack Risk Scale (ORACLE). Eur Respir J Open Res 2022;8(1)