What is the diagnostic approach for asthma in a child?

Diagnosing Asthma in Children Aged 5-16 Years

Do not diagnose asthma based on symptoms alone—the European Respiratory Society strongly recommends using a combination of objective tests including spirometry, bronchodilator reversibility testing, and fractional exhaled nitric oxide (FeNO) as first-line diagnostic tools, requiring at least two abnormal test results to confirm the diagnosis. 1, 2

Why Objective Testing is Essential

Misdiagnosis of asthma in children is alarmingly common, with over-diagnosis leading to unnecessary corticosteroid treatment and associated side effects, while under-diagnosis results in preventable morbidity, poor quality of life, and increased mortality. 1 Respiratory symptoms in children are frequently nonspecific and often represent viral respiratory tract infections rather than asthma. 1

Step 1: Clinical Assessment (But Don't Stop Here)

Key Symptoms to Document

• Wheeze is the most diagnostically useful symptom, with sensitivity of 55-86% and specificity of 64-90% for asthma. 2
• Cough and breathing difficulty are nonspecific and should never be used alone to diagnose asthma. 2
• Document symptom patterns including frequency, triggers, and response to previous treatments. 2

Critical Pitfall

Physicians correctly diagnose asthma based on clinical examination alone only 63-74% of the time, and symptoms correlate poorly with actual airway obstruction in one-third to one-half of patients. 3 This is why you must proceed to objective testing. 1

Step 2: First-Line Objective Testing (All Three Tests)

Spirometry

• Measure FEV1 and FEV1/FVC ratio. 2
• Abnormal results: FEV1 or FEV1/FVC less than lower limit of normal (LLN) and/or <80% predicted. 2
• Important: Normal spirometry does NOT exclude asthma, and abnormal spirometry alone does NOT confirm it. 2

Bronchodilator Reversibility (BDR) Testing

• Perform BDR testing even if spirometry is normal when clinical suspicion is high. 2
• A positive BDR indicates reversible airflow obstruction characteristic of asthma. 2

Fractional Exhaled Nitric Oxide (FeNO)

• Perform FeNO testing before spirometry. 2
• Cut-off: ≥25 ppb is considered elevated. 2
• Elevated FeNO suggests eosinophilic airway inflammation. 2

Step 3: Diagnostic Decision-Making

Confirm Asthma Diagnosis When:

At least two objective test results are abnormal, such as:

• Abnormal spirometry PLUS positive BDR, OR
• Abnormal spirometry PLUS elevated FeNO, OR
• Positive BDR PLUS elevated FeNO 2

When Diagnosis Remains Unclear:

• Consider peak expiratory flow rate (PEFR) variability with 2 weeks of twice-daily measurements; variability >12% suggests asthma. 2
• Use watchful waiting when initial tests are normal but clinical suspicion remains high, and repeat testing when the child is symptomatic. 2

Critical Pitfalls to Avoid

Never Diagnose Based On:

• Symptoms alone—this results in misdiagnosis in many children. 1, 2
• A single abnormal objective test—at least two abnormal results are required. 1
• Treatment response alone—do not diagnose asthma based solely on improvement after a trial of preventer medication. 2

Consider Alternative Diagnoses:

Before confirming asthma, rule out conditions that mimic it, including foreign body aspiration, vocal cord dysfunction, vascular rings, laryngotracheomalacia, enlarged lymph nodes, or tumors. 4 In younger children, consider cystic fibrosis and other congenital conditions. 5, 6

Age-Specific Considerations

These evidence-based recommendations specifically apply to children aged 5-16 years. 1, 2 Diagnosis in children under 5 years is particularly challenging due to difficulty obtaining objective lung function measurements and requires a different approach. 4, 6

The Bottom Line

The diagnostic algorithm requires:

1. Clinical assessment documenting wheeze and symptom patterns
2. All three first-line objective tests: spirometry, BDR, and FeNO
3. At least two abnormal test results to confirm diagnosis
4. Additional testing (PEFR variability) or watchful waiting if diagnosis remains unclear 2

This systematic approach prevents both over-diagnosis (avoiding unnecessary corticosteroid exposure) and under-diagnosis (preventing morbidity and mortality), directly improving quality of life outcomes. 1