What are the diagnostic criteria and treatment options for asthma?

Diagnosis of Asthma

Establish the Diagnosis Through Combined Clinical and Objective Testing

Asthma diagnosis requires both a compatible clinical history of variable respiratory symptoms AND objective confirmation of variable expiratory airflow limitation through pulmonary function testing, with at least two abnormal objective tests documented before confirming the diagnosis. 1

The diagnosis cannot be made on symptoms alone—objective testing is mandatory to avoid misdiagnosis. 1

Clinical History: Identify Characteristic Symptom Patterns

Look for these specific features that distinguish asthma from other conditions:

• Symptom variability: Wheeze, dyspnea, chest tightness, and cough that vary over time and in intensity 1
• Temporal patterns: Symptoms worse at night or early morning 2, 1
• Specific triggers: Exercise, allergens (pollens, dust, animals), cold air, or viral infections 2, 1
• Episodic nature: Recurrent episodes rather than constant symptoms 2

Critical pitfall: Normal physical examination between episodes is common and does not exclude asthma. 3 The medical history and physical examination alone are unreliable for establishing the diagnosis. 2

First-Line Objective Testing: Spirometry with Bronchodilator Reversibility

Spirometry is mandatory for all patients ≥5 years of age to establish the diagnosis objectively. 2, 1

Positive diagnostic criteria:

• FEV₁ improvement ≥12% AND ≥200 mL after bronchodilator administration 1
• If spirometry shows obstruction AND bronchodilator reversibility is positive, asthma is confirmed 1

When spirometry is normal or near-normal:

Proceed to second-line testing—normal spirometry does not exclude asthma, particularly in mild disease. 2, 4

Second-Line Testing: FeNO and Bronchial Challenge

Fractional Exhaled Nitric Oxide (FeNO):

• Diagnostic threshold: ≥25 ppb supports asthma diagnosis 1
• Measures airway inflammation directly 2
• When combined with abnormal spirometry or positive bronchodilator reversibility, confirms diagnosis 1

Bronchial Challenge Testing:

Use when asthma is suspected but spirometry and FeNO are normal or inconclusive. 2, 1

• Agents: Methacholine, histamine, cold air, or exercise challenge 2
• Interpretation: A positive test confirms airway hyperresponsiveness (characteristic of asthma); a negative test is more valuable to rule out asthma 2
• Safety requirement: Must be performed only by trained personnel in specialized facilities 2

Alternative Testing: Peak Flow Variability

Use only when spirometry and FeNO are non-diagnostic or unavailable:

• Positive result: ≥12% variability in peak expiratory flow 1
• Limitation: This is an inferior alternative to bronchial challenge testing due to wide variability in peak flow meters and reference values 2, 1
• Peak flow meters are designed for monitoring, not diagnosis 2

Diagnostic Algorithm Summary

1. Clinical history identifies characteristic variable respiratory symptoms with typical triggers and temporal patterns 2, 1
2. Spirometry with bronchodilator testing (first-line): If positive (≥12% and ≥200 mL improvement), diagnosis confirmed 1
3. If spirometry normal: Add FeNO testing (≥25 ppb supports diagnosis) 1
4. If both inconclusive: Bronchial challenge testing to detect airway hyperresponsiveness 2, 1
5. Require at least two abnormal objective tests before confirming diagnosis 1

Differential Diagnosis: Rule Out Alternative Conditions

When objective tests are negative, atypical, or response to treatment is poor, systematically evaluate:

In all age groups:

• Vocal cord dysfunction: Can mimic or coexist with asthma; look for variable flattening of inspiratory flow loop on spirometry; diagnosis requires direct visualization during an episode 2
• Gastroesophageal reflux disease: May coexist with asthma and complicate diagnosis 2

In adults:

• COPD: Use diffusing capacity testing—low DLCO increases probability of COPD and makes asthma much less likely 2, 4
• Congestive heart failure 2
• Pulmonary embolism 2
• Cough from ACE inhibitors 2

In children:

• Foreign body aspiration in trachea or bronchus 2
• Aspiration from swallowing dysfunction 2
• Vascular rings or laryngeal webs 2

Additional testing when differential diagnosis is unclear:

• Chest x-ray: To exclude structural abnormalities or other diagnoses 2
• Diffusing capacity: Helps distinguish COPD from asthma 2
• Inspiratory flow-volume loops: To evaluate for vocal cord dysfunction 2

Special Diagnostic Challenges

Cough-Variant Asthma:

• Cough is the principal or only manifestation 2
• Peak flow monitoring or bronchoprovocation may be helpful 2
• Diagnosis confirmed by positive response to asthma medications 2

Children Ages 0-4 Years:

• Diagnosis is challenging due to difficulty obtaining objective lung function measurements 2, 1
• Relies more heavily on clinical pattern recognition, which increases misdiagnosis risk 1
• Critical pitfall: Avoid inappropriate prolonged therapy, but also avoid underdiagnosing by using vague labels like "wheezy bronchitis" or "reactive airway disease" 2

Children Ages 5-16 Years:

• Apply the same diagnostic algorithm as adults: require at least two abnormal objective tests 1
• First-line tests: spirometry, bronchodilator reversibility, and FeNO 1
• Watchful waiting with repeat testing during symptomatic periods is acceptable when initial tests are inconclusive 1

When to Refer to a Specialist

Refer when:

• Initial objective tests fail to confirm diagnosis despite high clinical suspicion 1
• Symptoms persist despite treatment with normal objective tests 1
• Atypical features or diagnostic uncertainty are present 1
• Severe or difficult-to-control asthma requiring phenotyping for biologic therapies is suspected 1

Common Diagnostic Pitfalls to Avoid

• Never diagnose based on symptoms alone without objective testing 1
• Never rely on a single abnormal test—require at least two 1
• Never use symptom improvement after treatment as the sole diagnostic criterion 1
• Never assume normal spirometry excludes asthma—proceed to second-line testing 1
• Never overlook alternative diagnoses in patients with atypical presentations 1