What is the best approach to diagnose asthma in individuals of all ages with potential symptoms and triggers, considering their medical history and previous respiratory issues?

How to Check for Asthma

Asthma cannot be diagnosed by symptoms alone—you must obtain objective evidence of reversible airflow obstruction using spirometry in all patients aged 5 years and older. 1

Step 1: Identify Key Clinical Features

Begin by assessing for the cardinal symptom pattern:

• Recurrent wheeze is the single most important symptom, particularly if heard on auscultation or reported by the patient 1, 2
• Episodic cough (characteristically worse at night), shortness of breath, chest tightness, or difficulty breathing 1, 2
• Symptom variability is essential—symptoms must be episodic, not constant, and should vary by time of day, season, or in response to triggers 1, 3, 2

Critical triggers to ask about: 1, 3

• Exercise
• Viral respiratory infections
• Allergen exposure (pets, dust mites, pollen, mold)
• Irritants (tobacco smoke, strong odors, cold air)
• Weather changes
• Strong emotions (laughing, crying)

Important caveat: If chronic cough (>4 weeks) is the only symptom without wheeze, asthma is unlikely and alternative diagnoses should be pursued. 1

Step 2: Perform Focused Physical Examination

The physical exam is often completely normal between episodes, so a normal exam does not rule out asthma. 1, 2 When present, look for:

• Chest findings: Wheezing during normal breathing or prolonged forced expiration, hyperexpansion of thorax, use of accessory muscles, hunched shoulders 1, 2
• Upper airway findings: Increased nasal secretions, mucosal swelling, nasal polyps 1, 2
• Skin findings: Atopic dermatitis or eczema (suggests allergic phenotype) 1, 2

Step 3: Obtain Mandatory Spirometry (Age ≥5 Years)

Spirometry is essential and non-negotiable for diagnosis—history and physical examination alone are unreliable for confirming asthma or excluding alternatives. 1, 3

Spirometry Protocol:

1. Measure baseline FEV₁ and FEV₁/FVC ratio to document airflow obstruction 1, 3
2. Administer short-acting β₂-agonist (SABA) 1, 3
3. Repeat spirometry 10-15 minutes post-bronchodilator 1, 3

Diagnostic Criteria for Positive Test:

• FEV₁ increase ≥12% AND ≥200 mL from baseline confirms reversible airflow obstruction and supports asthma diagnosis 1, 3
• Some evidence suggests ≥10% of predicted FEV₁ may better differentiate asthma from COPD 1

Peak flow meters are NOT acceptable for diagnosis—they are designed for monitoring only, not diagnostic purposes, due to wide variability in devices and reference values. 1

Step 4: If Spirometry is Normal but Clinical Suspicion Remains High

When symptoms strongly suggest asthma but spirometry is normal (common in mild or well-controlled asthma), proceed to: 1, 3, 4

Option A: Bronchoprovocation Challenge Testing

• Methacholine challenge is the most common test for demonstrating airway hyperresponsiveness 1, 5
• Safety requirements: Must be performed by trained personnel with emergency equipment immediately available; contraindicated if baseline FEV₁ <60% predicted or <1.5 L in adults 5
• A positive test (≥20% fall in FEV₁) confirms airway hyperresponsiveness, a hallmark of asthma 1, 5
• Important limitation: Airway hyperresponsiveness can occur in other conditions, so positive test is not 100% specific for asthma 1

Option B: Two-Week Peak Flow Monitoring

• Document diurnal variation in peak expiratory flow >20% over 1-2 weeks 3, 2
• This demonstrates the characteristic variability of asthma 3

Option C: Trial of ICS with Repeat Testing

• In symptomatic patients with abnormal spirometry but negative bronchodilator response, consider 4-8 week trial of inhaled corticosteroids 1
• Must repeat objective testing (spirometry ± bronchodilator response) after the trial—improvement in symptoms alone is insufficient for diagnosis 1

Step 5: Systematically Exclude Alternative Diagnoses

You must actively rule out conditions that mimic asthma: 1, 3, 2

In Adults:

• COPD (especially if ≥10 pack-year smoking history, age >40, slowly progressive dyspnea, poor bronchodilator response) 1, 3, 2
• Vocal cord dysfunction (inspiratory stridor, normal spirometry, abnormal inspiratory flow-volume loop) 1, 2
• Congestive heart failure (orthopnea, paroxysmal nocturnal dyspnea, elevated BNP) 1
• ACE inhibitor-induced cough 1
• Gastroesophageal reflux with aspiration 1, 2

In Children:

• Foreign body aspiration (sudden onset, unilateral findings) 1, 2
• Cystic fibrosis (chronic productive cough, failure to thrive, recurrent infections) 1
• Vascular rings or laryngeal webs 1

Additional Testing When Differential Diagnosis is Unclear:

• Diffusing capacity (DLCO): Low DLCO suggests COPD rather than asthma 1, 3
• Chest X-ray: Excludes pneumonia, heart failure, structural abnormalities 3, 2
• Flow-volume loops: Evaluate for vocal cord dysfunction (flattened inspiratory loop) 1, 3

Step 6: Consider Adjunctive Tests

Allergy Testing:

• Identify clinically important allergen sensitivities to guide allergen avoidance and consider immunotherapy 3, 6
• Particularly useful in patients with allergic phenotype (atopic dermatitis, allergic rhinitis, family history of atopy) 1, 2

Fractional Exhaled Nitric Oxide (FeNO):

• Elevated FeNO supports diagnosis of allergic/eosinophilic asthma 3, 4
• Can help differentiate asthma from COPD in smokers 4

Critical Pitfalls to Avoid

1. Never diagnose asthma on symptoms alone—this is a strong recommendation against doing so based on moderate-quality evidence 1

2. Do not skip spirometry because the patient "seems like asthma"—physicians correctly diagnose asthma based on clinical examination alone only 63-74% of the time 7

3. Recognize that normal physical exam does not exclude asthma—most patients are normal between episodes 1, 2, 8

4. Do not use peak flow meters for diagnosis—they lack the accuracy and standardization required 1

5. If baseline spirometry is inaccurate or not performed, you may underestimate initial FEV₁ and miss significant bronchoconstriction during challenge testing, leading to dangerous over-dosing 5

6. In patients already on ICS-containing medications, standard diagnostic criteria may not apply—consider supervised step-down of treatment and repeat objective testing 1

Special Population: Children Under 5 Years

Definitive diagnosis is difficult due to inability to perform spirometry. 2 In this age group:

• Diagnosis relies heavily on clinical pattern of recurrent wheeze heard by healthcare professional on auscultation 2
• Consider trial of asthma therapy with careful reassessment 2
• Formal objective testing should be performed once child reaches age 5 years 1