Diagnosis of asthma

BTS/SIGN Asthma guideline, July 2019

BTS/SIGN Asthma guideline, July 2019

DIAGNOSTIC TRIAD

  1. SYMPTOMS

    Wheeze, breathlessness, chest tightness, cough

  2. VARIABLE AIRFLOW OBSTRUCTION

  3. EOSINOPHILIC AIRWAY INFLAMMATION or ATOPY

OTHER FEATURES THAT INCREASE PROBABILITY OF ASTHMA DIAGNOSIS

  1. Triggers: recurrent wheeze with exercise, viral infection, cold air, allergens, emotion/laughter, NSAIDs/Beta-blockers

  2. Variability of recorded PEF and FEV1: lower values when symptomatic compared with asymptomatic

  3. Personal history of atopy: eczema/dermatitis/allergic rhinitis, raised allergen-specific IgE levels, positive skin-prick tests to aeroallergens or blood eosinophilia

  4. Diurnal symptom variability: worse at night/early morning

OBJECTIVE TESTS OF ASTHMA

VARIABLE AIRFLOW OBSTRUCTION

Peak expiratory flow (PEF) charting of variability
More than 20% variability in multiple daily PEF recordings (≥2) is regarded as a positive result for the diagnosis of asthma.

Occupational asthma: serial peak flow four times a day for three weeks at home and at work is a diagnostic test of proven value.
Suitable record forms can be downloaded from http://www.occupationalasthma.com.   

Spirometry with Bronchodilator reversibility (BDR) [PREFERRED INITIAL TEST]
May be performed in children aged>5yr
Obstructive spirometry diagnosed if FEV1/FVC ratio less than 70%.
Bronchodilator Reversibility: an improvement in FEV1 ≥ 12% in response to beta-2 agonists or corticosteroids is regarded as a positive result

Challenge Test: direct bronchial challenge test with histamine or methacholine
A PC20 value (provocative concentration causing a 20% drop in FEV1) of 8 mg/ml or less is regarded as a positive result.

EOSINOPHILIC AIRWAY INFLAMMATION or ATOPY

Fractional exhaled nitric oxide (FeNO) testing
Confirms eosinophilic airway inflammation
Test deemed positive (abnormal) if FeNO level ≥40 ppb in steroid-naive adults OR FeNO level ≥35 ppb in children
Approximately 1 in 5 people with a negative FeNO will have asthma (20% False-negative rate)
Approximately 1 in 5 people with a positive FeNO will not have asthma (20% False-positive rate)

Blood tests
Positive if blood eosinophilia ≥ 4%
Raised allergen-specific IgE

MANAGEMENT

1. HIGH PROBABILITY OF ASTHMA based on symptoms, variability and atopy:

Code as suspected asthma and initiate 6w inhaled corticosteroids + reliever B2 agonist

Monitor and assess response:
Spirometry FEV1/ at clinic visits
Validated symptom questionnaire
Domiciliary serial PEFs with/without symptoms

If good response, asthma diagnosis confirmed and will need adjustment of maintenance dose, self-management advice and on-going monitoring

2. INTERMEDIATE PROBABILITY OF ASTHMA

Undertake OBJECTIVE TESTS OF ASTHMA: variable airflow obstruction (e.g. spirometry with bronchodilator reversibility) AND eosinophilic airway inflammation

Red-flag signs suggesting alternative diagnosis and referral to a respiratory physician

Adults

  • Severe/life-threatening asthma attack

  • Prominent systemic features (such as myalgia, fever, and weight loss)

  • Unexpected clinical findings (such as crackles, finger clubbing, cyanosis, evidence of cardiac disease, monophonic wheeze, or stridor).

  • Persistent non-variable breathlessness

  • Chronic sputum production

  • Unexplained restrictive spirometry

  • Chest X-ray shadowing

  • Marked blood eosinophilia

  • Suspected occupational asthma (symptoms improve away from work) in high-risk occupations

Children

  • Failure to thrive

  • Unexplained clinical findings (such as focal signs, abnormal voice or cry, dysphagia, and/or inspiratory stridor)

  • Symptoms that are present from birth or perinatal lung problem

  • Excessive vomiting or posseting

  • Severe upper respiratory tract infection

  • Persistent wet or productive cough

  • Family history of unusual chest disease

  • Nasal polyps

Differential diagnosis

  • Bronchiectasis: copious sputum, frequent chest infections, a history of childhood pneumonia, and coarse lung crepitations

  • Chronic obstructive pulmonary disease (COPD): asthma and COPD can be difficult to distinguish clinically and may co-exist. Clinical features of COPD include a productive cough and dyspnoea on exertion in a person over 35 years of age who is a current or previous smoker.

  • Ciliary dyskinesia: persistent moist cough present from birth.

  • Cystic fibrosis: persistent moist cough and gastrointestinal symptoms from birth, and failure to thrive in children.

  • Dysfunctional breathing: breathlessness, dizziness, light-headedness, and peripheral tingling.

  • Foreign body aspiration: sudden-onset cough, stridor (upper airway) or reduced chest wall movement on the affected side, bronchial breathing, and reduced or diminished breath sounds (lower airway).

  • Gastro-oesophageal reflux: cough, postural and food-related symptoms, and vomiting

  • Heart failure: orthopnoea, oedema, history of ischaemic heart disease, and fine lung crepitations

  • Interstitial lung disease: asbestosis, pneumoconiosis, fibrosing alveolitis, sarcoidosis — dry cough and fine lung crepitations

  • Lung cancer: cough, haemoptysis, weight loss, or persistent hoarse voice

  • Pertussis: paroxysms of coughing, vomiting after coughing, or an inspiratory whoop, cough may persist for several months

  • Pulmonary embolism (PE): acute-onset breathlessness, pleuritic pain, haemoptysis, crackles, and sinus tachycardia

  • Tuberculosis: persistent productive cough, which may be associated with breathlessness and haemoptysis.

  • Upper airway cough syndrome: frequent throat clearing and chronic sinusitis or allergic rhinitis

  • Vocal cord dysfunction: dyspnoea and stridor

Dr Rajesh VarmaAsthma diagnosis