What is the approach to diagnose asthma in pediatric patients?

Diagnosing Asthma in Children Aged 5-16 Years

Never diagnose asthma in children based on clinical history alone or following a single abnormal objective test—the European Respiratory Society strongly recommends using a combination of spirometry, bronchodilator reversibility testing, and fractional exhaled nitric oxide (FeNO) measurement as first-line diagnostic tests. 1

Why Clinical History Alone Fails

Relying solely on symptoms leads to substantial misdiagnosis rates in children because respiratory symptoms are common and nonspecific in this age group, frequently representing viral respiratory tract infections rather than asthma. 1 Over-diagnosis results in unnecessary corticosteroid treatment with associated side effects and healthcare costs, while under-diagnosis causes preventable morbidity, poor quality of life, and increased mortality in low-resource settings. 1

The Three Essential First-Line Tests

1. Spirometry

• Perform spirometry in all children aged 5 years and older suspected of having asthma. 2, 3
• Look for FEV1/FVC <80% or below the lower limit of normal (LLN), or FEV1 <80% predicted. 3
• Critical caveat: Normal spirometry does NOT exclude asthma—if clinical suspicion remains high despite normal spirometry, proceed to bronchial challenge testing or 2-week peak flow monitoring. 2, 3

2. Bronchodilator Reversibility (BDR) Testing

• Strongly recommended in all children with abnormal spirometry. 3
• Diagnostic threshold: FEV1 increase ≥12% AND/OR ≥200 mL after short-acting beta-agonist inhalation. 3
• Important pitfall: BDR <12% does not exclude asthma—some children with genuine asthma will not demonstrate reversibility at a single testing session. 3

3. Fractional Exhaled Nitric Oxide (FeNO)

• Strongly recommended as part of the diagnostic work-up. 3
• Diagnostic threshold: FeNO ≥25 ppb supports asthma diagnosis. 3
• FeNO has the highest area under the curve (0.80) among diagnostic tests for pediatric asthma. 4
• Caveat: FeNO <25 ppb does not exclude asthma, particularly non-allergic phenotypes. 3

Diagnostic Algorithm

Step 1: Identify Characteristic Symptom Patterns

• Recurrent episodes of wheeze (most important symptom), cough, difficulty breathing, or chest tightness. 2, 3
• Symptom variability: diurnal variations, seasonal patterns, episodic nature. 2
• Trigger-induced symptoms: exercise, cold air, allergen exposure, irritants. 2
• Family history of asthma, allergies, or atopic disorders. 2

Step 2: Perform All Three First-Line Objective Tests

• Spirometry with pre- and post-bronchodilator testing. 2, 3
• FeNO measurement. 3
• Document results from all three tests—do not stop after one positive result. 1

Step 3: Interpret Results in Combination

• If spirometry shows obstruction (FEV1/FVC <80%) AND BDR is positive (≥12% increase), diagnosis is strongly supported. 3
• If FeNO ≥25 ppb in addition to positive spirometry/BDR, diagnosis is further confirmed. 3
• If all three tests are normal but clinical suspicion remains high: Proceed to bronchial challenge testing (methacholine or exercise) or 2-week peak expiratory flow rate variability monitoring. 1, 2

Step 4: Systematically Exclude Alternative Diagnoses

• In children, consider foreign body aspiration, cystic fibrosis, vocal cord dysfunction. 2
• Order chest X-ray to exclude pneumonia, structural abnormalities, or other pathology. 2

Role of Allergy Testing

Do NOT use allergy testing to diagnose asthma—skin-prick tests have low specificity (23-40%) and specific IgE tests have low specificity (56-65%) for asthma diagnosis. 3 However, allergy testing is useful AFTER asthma diagnosis for phenotyping, planning individualized prevention measures, and identifying potential allergic triggers. 3

Additional Diagnostic Tests (Second-Line)

If first-line tests are inconclusive:

• Bronchial challenge testing (methacholine or exercise) has high diagnostic accuracy (AUC 0.81 for methacholine, 0.74 for exercise). 4
• 2-week peak expiratory flow rate (PEFR) variability test can demonstrate characteristic asthma patterns. 1

Common Pitfalls to Avoid

• Never diagnose based on a single abnormal test—this leads to high misdiagnosis rates. 1
• Never assume normal spirometry excludes asthma—many children with genuine asthma have normal lung function between exacerbations. 3
• Never skip objective testing in favor of a "trial of treatment"—this approach was specifically excluded as a diagnostic criterion by the European Respiratory Society task force. 1
• Never use allergy testing alone to diagnose asthma—this will miss all non-allergic asthma cases. 3

Special Considerations for Preschool Children (<5 Years)

For children aged 1-5 years where spirometry is not feasible, diagnosis requires frequent asthma-like symptoms (≥8 days/month) or recurrent exacerbations (≥2), plus objective documentation of airflow obstruction signs or convincing parent-reported symptoms with improvement on asthma therapy, and no clinical suspicion of alternative diagnosis. 5 The characteristic feature is wheezing, commonly accompanied by difficulty breathing and cough. 5