Diagnosis in Adults

The British guidelines state that asthma is a clinical diagnosis since no single test, sign or symptom is specific enough to confirm the diagnosis.

Although the majority of cases are diagnosed in childhood, approximately 1 in 4 patients are not diagnosed with asthma until adulthood. A number of factors and test results are considered before the diagnosis is made by the GP or respiratory specialist.

Clinical features that increase the probability of asthma in adults [2]
  • More than one of the following symptoms: wheeze, cough, difficulty breathing, chest tightness, particularly if the symptoms:
    • Are worse at night/early morning
    • Ocur in response to exercise, allergen exposure or cold air
    • Are triggered by aspirin or beta-blockers
    • Occur in the absence of a cold
  • Personal or family history of atopic disorder or asthma
  • Widespread wheeze on chest auscultation
  • Otherwise unexplained low FEV1 or PEFR
  • Otherwise unexplained peripheral blood eosinophilia
Clinical features that decrease the probability of asthma in adults [2]
  • Symptoms with colds only
  • Chronic productive cough without wheeze or breathlessness
  • Dizzyness, light-headedness or paraesthesia peripherally
  • Voice disturbance
  • Cardiac disease
  • Significant smoking history (>20 pack years)
  • Repeated normal chest examination when symptomatic
  • Repeatedly normal PEFR or spirometry when symptomatic

The probability of asthma

Patients with a high probability of asthma

Patients with a high probability of asthma are treated accordingly – see next page.

Patients with an intermediate probablity of asthma

For patients with an intermediate probability of asthma, some of the following tests may be required to elucidate whether asthma is responsible for their symptoms:

  • Spirometry/ PEFR

An FEV1/FVC <0.7 is strongly suggestive of asthma. Spirometry has significant advantages over PEFR in the stable setting. The result is less effort dependent than PEFR, normal ranges are more robust and airway obstruction can be clearly documented. A PEFR meter is portable and useful for self monitoring (particularly when occupational asthma is suspected) and in the acute setting.

  • Treatment trials and reversibility testing

A 400ml improvement in FEV1 (or 60l/min. increase in PEFR) in response to either of the following strongly suggests underlying asthma:

  • 400 mcg inhaled salbutamol
  • 6-week trial of steroid inhaler (beclometasone 200 mcg bd or equivalent)
  • Tests that may be requested be respiratory specialists

The following tests have a high sensitivity but moderate specificity for asthma:

  • Eosinophil count in sputum (eosinophilic inflammation)
  • Exhaled nitric oxide concentration (eosinophilic inflammation)
  • Methacholine or histamine challenge (airway hyper-responsivity)

Although these tests can be useful in the diagnosis of asthma, their continued monitoring is not supported by evidence and improvement does not imply a greater level of asthma control.

  • Routine use of FeNO testing in adults or children except in specialist asthma clinics. The test involves measuring an individuals fractional exhaled nitric oxide – a gas found in slightly higher levels in people with asthma. An increase may suggest some inflammation of the airways and supports, but doesnt prove, a diagnosis of asthma. The available evidence was inconsistent on how effective the test was in delivering different positive outcomes indicating better asthma control.
  • Routine use of a sputum eosinophilia test – a specific test to assess ‘biomarkers’ of inflammation in a patient’s spit – in order to monitor asthma in adults or children.