What is the diagnostic approach for a patient presenting with symptoms suggestive of asthma, such as wheezing, shortness of breath, or cough, especially if these symptoms are recurrent or worsen with specific triggers?

Diagnosis of Asthma

Asthma is a clinical diagnosis established when episodic symptoms of airflow obstruction or airway hyperresponsiveness are present, airflow obstruction is at least partially reversible, and alternative diagnoses are excluded. 1

Key Clinical Features to Identify

The diagnosis requires recognition of characteristic symptom patterns rather than any single confirmatory test 1:

• Wheezing (diffuse, polyphonic, bilateral, particularly expiratory) - this is a cardinal sign that must be documented when present 1
• Recurrent cough, shortness of breath, or chest tightness 1
• Variable and intermittent symptoms - this is the clinical hallmark 1, 2
• Nocturnal worsening 1
• Trigger-provoked symptoms including exercise, allergens, viral infections, cold air, or irritants 1, 3

Essential Diagnostic Components

History Elements

Document these specific factors 1:

• Pattern of symptoms: perennial vs. seasonal; continual vs. episodic; diurnal variations 1
• Precipitating factors: allergic triggers, exercise, cold air, respiratory infections 1
• Personal or family history of asthma, eczema, or allergic rhinitis 1
• Medication responses: worsening with aspirin/NSAIDs or beta-blockers 1

Physical Examination

Focus on 1:

• Upper respiratory tract
• Chest examination (listen for wheeze during exacerbations)
• Skin (atopic dermatitis)

Critical caveat: Between episodes, physical examination may be completely normal 1. Normal findings do not exclude asthma.

Objective Testing Requirements

Spirometry (Age ≥5 Years)

Spirometry is required for diagnosis in patients 5 years or older 1:

• Measure FEV1 and FEV1/FVC ratio 1
• Document reversibility: ≥12% and ≥200 mL improvement in FEV1 after bronchodilator 4, 5
• Baseline FEV1 must be ≥60% predicted to safely proceed with further testing 6

Important pitfall: Spirometry may be normal between episodes in mild asthma 1, 7. If repeatedly normal despite symptoms, the diagnosis must be questioned, but cannot be excluded based on this alone 1.

Peak Expiratory Flow (PEF) Monitoring

When spirometry is unavailable or normal 1, 5:

• Serial PEF measurements showing variability support the diagnosis 1
• ≥20% diurnal variation or improvement after bronchodilator suggests asthma 1, 5

Bronchial Provocation Testing

Methacholine challenge is indicated when spirometry is normal (FEV1 ≥70% predicted) but clinical suspicion remains high 6, 5:

• Contraindicated if baseline FEV1 <60% predicted or <1.5 L in adults 6
• Not recommended in patients with clinically apparent asthma or active wheezing 6
• Positive test: ≥20% reduction in FEV1 from post-diluent baseline 6
• Must have emergency bronchodilator and equipment immediately available 6

Additional Biomarkers

Consider measuring 7, 4, 5:

• Fractional exhaled nitric oxide (FeNO): ≥35 ppb suggests type 2 inflammation and increases probability of allergic asthma 7, 5
• Blood eosinophils: ≥150/μL identifies eosinophilic phenotype 5
• Allergy testing: Identify clinically important allergen sensitivities 4

Diagnostic Pathway When Initial Testing Is Inconclusive

If clinical symptoms suggest asthma but objective testing doesn't meet standard criteria 5:

1. Do not rely solely on cutoff values to exclude asthma 5
2. Consider diagnostic anti-inflammatory therapy (trial of ICS) if any of these are present 5:
   • Positive PEF bronchodilator response (≥20% improvement)
   • FEV1 variability ≥12% and ≥200 mL between visits
   • Small airway dysfunction with elevated FeNO (≥35 ppb)
3. Document response to therapy - improvement supports the diagnosis 8, 7

Excluding Alternative Diagnoses

Perform additional testing as needed 1:

• Chest radiography to exclude other pathology 1
• Diffusing capacity (DLCO) in smokers: low DLCO makes COPD more likely and asthma less likely 7
• Consider vocal cord dysfunction, COPD, bronchiectasis, cardiac disease, or pulmonary embolism based on clinical context 1

Common Diagnostic Pitfalls

• Atypical presentations: Some patients present with cough alone (cough-variant asthma) without audible wheezing 1, 8, 9
• Occupational asthma: Suspect in all adult-onset cases; symptoms improve away from work 8
• Poor response to standard therapy: If symptoms don't improve with appropriate asthma medications, reconsider the diagnosis 8
• Smokers with symptoms: May have asthma, COPD, or both (ACO); normal post-bronchodilator spirometry rules out COPD 7, 5