Section 1:

The definition and diagnosis of asthma

The diagnosis of asthma is a clinical one.1 Central to the definition of asthma is the presence of symptoms – wheeze, breathlessness, chest tightness, cough – and of variable airflow obstruction.1

There is no single diagnostic test for asthma: diagnosis is based on the recognition of a characteristic pattern of respiratory symptoms and signs, the absence of any alternative explanation for symptoms and signs, and supported by objective tests.1

A patient attending the pharmacy with a diagnosis of asthma should have had a structured clinical assessment in their GP surgery. This will include:

  • A history of recurrent episodes of symptoms, ideally corroborated by variable peak flows when symptomatic and asymptomatic;
  • Symptoms of wheeze, cough, breathlessness and chest tightness that vary over time;
  • Recorded observation of wheeze confirmed by a healthcare professional on auscultation;
  • Personal/family history of other atopic conditions;
  • No symptoms, signs or clinical history to suggest alternative diagnoses, such as chronic obstructive pulmonary disease (COPD), dysfunctional breathing, physical inactivity or obesity.

Objective tests used to support a possible diagnosis of asthma include:

  • Spirometry and bronchodilator reversibility: in patients with obstructive spirometry, an improvement in forced expiratory volume in 1 second (FEV1) of >12% in response to either β2 agonists or corticosteroid treatment trials, together with an increase in volume of 200 ml or more is considered a positive test. An improvement of >400 ml in FEV1 strongly suggests asthma. In children, an improvement in FEV1 of >12% is regarded as a positive test.1
  • Peak expiratory flow (PEF) – PEF variability is calculated as the difference between the highest and lowest PEF measurements, expressed as a percentage of the average (usually around 20% if using four or more readings per day).1
  • Fractional exhaled nitric oxide (FeNO) – a non-invasive test to detect eosinophilic inflammation in the airways. In steroid-naïve patients, a FeNO level of 40 parts per billion (ppb) in adults and 35 ppb in children is considered a positive test. However, FeNO levels may be increased in patients with hayfever but reduced in cigarette smokers, for example.1
  • Referral for challenge tests should be considered for patients with no evidence of airflow obstruction on initial assessment but for whom asthma remains a possibility.1

Diagnostic tests are usually performed at a single point in time whereas asthma status is variable. Objective tests performed when a patient is asymptomatic may produce a ‘false negative’ result. Tests performed when a patient is asymptomatic can be compared with those undertaken when a patient is symptomatic to detect variation over time.1

Job code: UK/RES-19014c DOP: February 2020

References

  1. British Thoracic Society/Scottish Intercollegiate Guidelines Network (BTS/SIGN) British Guideline on the Management of Asthma; 24 July 2019. https://www.brit-thoracic.org.uk/quality-improvement/guidelines/asthma/ [Accessed February 2020]