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The editorial content below has been developed solely between Guidelines in Practice and the expert author.

holmes steve

Guest Editor—Dr Steve Holmes

GP, Park Medical Practice, Shepton Mallet 

Since the latest update to the BTS/SIGN British guideline on the management of asthmawas issued in 2016, new guidance on the diagnosis and management of asthma was published by NICE in 2017. This email considers what the guidelines recommend about diagnosing asthma and provides advice on how to implement the recommendations in primary care.

The well established British Thoracic Society/Scottish Intercollegiate Guidelines Network (BTS/SIGN) guideline on the management of asthma was updated in 20161 and the NICE guidance on the diagnosis, monitoring, and management of asthma was published in 2017.2

Both guidelines include recommendations on asthma diagnosis, aiming to ensure that a diagnosis of asthma is made as robustly as possible. While the similarities between the guidelines are greater than the differences, the recommendations on asthma diagnosis differ between the two guidelines. These differences, and what this means for implementing the guidelines in primary care, will be considered in this email.

Diagnosis: key points from the BTS/SIGN guideline

The BTS/SIGN guideline recommends that the initial assessment should include a good history and examination, looking out for key features.1 If a diagnosis of asthma appears likely (high probability) then a therapeutic trial of inhaled corticosteroid (ICS) is suggested for 6 weeks, with an assessment of lung function and a validated symptom questionnaire before and after treatment.1

If treatment appears effective, then a diagnosis can be made and treatment subsequently monitored.1

Both the BTS/SIGN and NICE guidelines highlight the importance of considering occupation and other potential triggers in a person with a new diagnosis, or, if asthma appears to recur after a period of natural resolution.1,2

If the diagnosis is unclear

If the diagnosis is unclear, the BTS/SIGN guideline suggests that more testing should be considered to guide diagnosis. This would include testing for reversibility (possible with challenge testing or serial peak flow readings) and testing for evidence of airway inflammation (fractional exhaled nitric oxide [FeNO] or blood eosinophil measurement).1

The BTS/SIGN guideline also reminds clinicians that if a patient has symptoms and signs that suggest the condition is not asthma and may be something else, it should not be treated or diagnosed as asthma.1

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Click here to view the Guidelines summary of the BTS/SIGN guideline on the management of asthma in adults—including an algorithm for diagnosis

Diagnosis: key points from the NICE guideline

Compared with BTS/SIGN, the NICE guideline takes a more objective approach to making an asthma diagnosis, with less emphasis on the therapeutic trial and clinical judgement.1,2

Incidentally, NICE also recommends that patients should have skin prick testing to aeroallergens or specific immunoglobulin E tests to identify triggers after the diagnosis of asthma has been made, a recommendation that BTS/SIGN does not address.1,2

NICE has suggested that commissioners should establish asthma diagnostic hubs to achieve economies of scale and improve the practicalities of implementing the recommendations.2

FeNO testing

The NICE guideline includes an algorithm on objective tests for people with suspected asthma, which recommends the use of FeNO and spirometry—unless the patient has acute asthma, which should be treated first.2

NICE states that asthma should be diagnosed in people with suggestive symptoms of asthma (although makes no mention of examination findings), with one of:

  • FeNO ≥40 parts per billion (ppb) and:
    • positive bronchodilator reversibility or
    • positive peak flow variability or
    • bronchial hyperreactivity on testing
  • FeNO = 25–39 ppb and a positive bronchial challenge test
  • positive bronchodilator reversibility and positive peak flow variability irrespective of FeNO level.


NICE recommends that spirometry and a bronchodilator reversibility test should be performed if the patient has a forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) ratio <70% (or below the lower limit of normal [LLN] if this is available).2

Introducing FeNO into UK hospitals, let alone primary care, requires significant initial investment. It is perhaps surprising that this recommendation was not the other way round; most computerised, quality assured spirometry would include the LLN and expecting those performing spirometry to use the LLN would capture the recognised underdiagnosis in younger people using a fixed ratio.3

Both NICE and BTS/SIGN define significant reversibility as an improvement in FEV1 of ≥12% and an increased volume of ≥200 ml.1,2

Peak flow variability

NICE is quite specific about when to monitor peak flow variability for 2–4 weeks as part of the diagnostic pathway; it is considered appropriate when there is:2

  • obstructive spirometry
  • negative bronchodilator reversibility testing
  • a FeNO level of 25–39 ppb (a FeNO level ≥40 ppb is thought to be strongly suggestive of asthma in the diagnosis algorithm).

NICE suggests that ≥20% variability is a positive test in peak flow variability testing (using four tests per day).2

Monitoring asthma control

The NICE guidance makes useful recommendations on the use of FeNO for monitoring asthma control, suggesting this should not be used for routine monitoring but should be used in people who are symptomatic despite using ICS.2

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Click here to view the Guidelines summary of the NICE asthma diagnosis and monitoring guideline—including algorithms for assessment

Learning points for asthma diagnosis

  • Acute asthma symptoms should be treated before further investigative tests2

  • BTS/SIGN recommends that if a therapeutic trial of ICS for 6 weeks appears effective, a diagnosis of asthma can be made1

  • Testing for reversibility and evidence of airway inflammation can help confirm an unclear diagnosis1

  • It is important to consider occupation and other potential triggers in a person with a new diagnosis of asthma1,2

  • A FeNO level ≥40 ppb is strongly suggestive of asthma2

  • Significant reversibility is defined as an improvement in FEV1 of ≥12% and an increased volume of ≥200 ml1,2

  • Peak flow variability for 2–4 weeks should be undertaken when there is obstructive spirometry but negative bronchodilator reversibility testing and a FeNO level of 25–39 ppb2

  • FeNO can be used to monitor asthma control in people who are symptomatic despite using inhaled corticosteroids.2


  1. British Thoracic Society, Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma. SIGN 153. BTS/SIGN, 2016. Available at:

  2. NICE. Asthma: diagnosis, monitoring and chronic asthma management. NICE Guideline 80. NICE, 2017. Available at:

  3. Swanney M, Ruppel G, Enright P et al. Using the lower limit of normal for the FEV1/FVC ratio reduces the misclassification of airway obstruction. Thorax 2008; 63 (12): 1046–1051.

Making good asthma care better: lessons from the NRAD