What is the initial workup for a patient with suspected asthma?

Initial Workup for Suspected Asthma

The initial workup for suspected asthma requires obtaining a detailed medical history focused on episodic respiratory symptoms, performing spirometry with bronchodilator testing in all patients ≥5 years old to demonstrate reversible airflow obstruction, and considering allergy testing in patients with persistent symptoms. 1

Medical History - Key Elements to Document

The history must establish recurrent episodes of airflow obstruction by documenting: 1

• Specific symptom patterns: Wheezing, chest tightness, shortness of breath, and cough that are episodic and variable over time 1, 2
• Temporal patterns: Symptoms worse at night or early morning, improvement on weekends/holidays, and worsening with return to specific environments 1
• Trigger identification: Exercise, allergen exposure (pollens, dust, animals), viral infections, irritants (smoke, strong odors), weather changes, and emotional stress 1, 3
• Quantifiable impairment measures: Frequency of daytime symptoms per week, nighttime awakenings per week, activity limitations, and rescue medication use (specifically days per week of short-acting beta-agonist use) 4
• Risk assessment: History of exacerbations requiring oral corticosteroids, emergency department visits, hospitalizations, or intensive care admissions 4, 5
• Complete occupational history: Detailed work exposures at symptom onset, new materials introduced before symptoms, coworker exposures, and improvement away from workplace 1
• Personal and family history: Atopic conditions (eczema, allergic rhinitis), family history of asthma or atopy 3

Physical Examination Findings

While physical examination alone is insufficient for diagnosis (physicians correctly diagnose asthma based on clinical examination only 63-74% of the time), examine for: 2

• Respiratory signs: Wheezing, prolonged expiratory phase, use of accessory muscles, increased respiratory rate 1, 2
• Associated atopic conditions: Nasal polyps, allergic rhinitis, atopic dermatitis 1

Critical caveat: Absence of wheezing does not exclude asthma, and the presence of wheezing does not confirm it—objective testing is mandatory. 1, 2

Spirometry - The Essential Diagnostic Test

Spirometry must be performed in all patients ≥5 years old with suspected asthma within 24 hours of symptoms or workplace exposure to avoid false-negative results. 1

Bronchodilator Reversibility Testing

• Measure baseline FEV₁ and FVC 1
• Administer short-acting bronchodilator (typically 4 puffs of albuterol via spacer) 1
• Repeat spirometry 15 minutes post-bronchodilator 1
• Positive test: ≥12% AND ≥200 mL improvement in FEV₁ strongly supports asthma diagnosis 4, 6

If Spirometry is Normal

When spirometry is normal but asthma is still suspected clinically: 1, 6

• Bronchoprovocation testing with methacholine, histamine, cold air, or exercise challenge can identify airway hyperresponsiveness 1, 3
• A positive bronchoprovocation test is consistent with asthma but can occur in other conditions 1
• A negative test is more useful to rule out asthma 1
• Testing must be performed by trained personnel due to safety concerns 1

Peak Expiratory Flow (PEF) Monitoring

While spirometry is preferred for diagnosis, PEF monitoring can support the diagnosis: 1, 7

• Diurnal variability >20% between best and worst readings over 1-2 weeks establishes asthma diagnosis 4, 7
• Requires measurements at least 4 times daily in triplicate during work weeks and periods away from suspected exposures (minimum 10 days) 1
• Peak flow meters are designed for monitoring, not as primary diagnostic tools due to wide variability in devices and reference values 1

Allergy Testing - When to Perform

Perform skin testing or specific IgE blood tests in patients with persistent asthma who require daily controller medications to identify perennial indoor allergens. 1, 4

Test for: 4

• House dust mite
• Cockroach
• Cat and dog dander
• Mold
• Other relevant environmental allergens based on exposure history

Additional Testing - Selective Use

These tests are not routinely necessary but useful when considering alternative diagnoses: 1

• Chest radiograph: To exclude pneumothorax, consolidation, pulmonary edema, foreign body, or tumor 1
• Complete blood count: May show eosinophilia suggesting allergic component 1
• Exhaled nitric oxide (FeNO): High levels increase probability of allergic asthma 6
• Diffusing capacity (DLCO): Low DLCO increases probability of COPD and makes asthma much less likely in adults with smoking history 6

Critical Differential Diagnoses to Consider

The workup must actively exclude: 1

In children:

• Vocal cord dysfunction
• Foreign body aspiration
• Vascular rings or laryngeal webs
• Gastroesophageal reflux with aspiration

In adults:

• COPD (chronic bronchitis/emphysema) - distinguished by low post-bronchodilator DLCO 6
• Congestive heart failure
• Vocal cord dysfunction - look for flattening of inspiratory flow loop on spirometry 1
• Medication-induced cough (ACE inhibitors)
• Pulmonary embolism

Common Diagnostic Pitfalls

• Relying on symptoms alone: Symptoms correlate poorly with airway obstruction in one-third to one-half of patients 2
• Single normal spirometry: Patients with mild asthma commonly have normal spirometry when asymptomatic—repeat testing during symptoms or perform bronchoprovocation 1, 6
• Testing too long after exposure: Spirometry and bronchoprovocation may normalize >24 hours after workplace or trigger exposure 1
• Misdiagnosing occupational asthma: Requires detailed occupational history and objective testing, not just symptom patterns 1
• Missing vocal cord dysfunction: Can mimic or coexist with asthma; suspect in difficult-to-treat cases and elite athletes with exercise symptoms unresponsive to asthma medications 1