How is asthma diagnosed in a child?

Diagnosing Asthma in Children Aged 5-16 Years

Asthma diagnosis in children aged 5-16 years requires objective testing with spirometry, bronchodilator reversibility (BDR) testing, and exhaled nitric oxide fraction (FeNO) as first-line tests—never diagnose based on symptoms alone. 1

Core Diagnostic Principle

The 2021 European Respiratory Society guidelines provide the most comprehensive, evidence-based approach and strongly recommend against diagnosing asthma based on clinical symptoms alone (strong recommendation, moderate quality evidence). 1 This is critical because wheeze has only 55-86% sensitivity and 64-90% specificity for asthma—meaning symptoms alone lead to misdiagnosis in a substantial number of children. 1

Algorithmic Approach to Diagnosis

Step 1: Recognize Key Symptoms (But Don't Stop Here)

• Recurrent wheeze (reported by parents or heard on auscultation) is the most important symptom 1
• Cough and breathing difficulty are nonspecific and should not be used alone to diagnose asthma 1
• Important caveat: Children with chronic cough (>4 weeks) as the only symptom are unlikely to have asthma and require alternative investigation 1

Step 2: Perform Objective Testing (Required)

First-line tests (all recommended):

1. Spirometry (strong recommendation, moderate quality evidence) 1

   • Look for FEV₁/FVC <80% or <LLN (lower limit of normal)
   • Or FEV₁ <80% predicted or <LLN
   • Critical point: Normal spirometry does NOT exclude asthma 1

2. Bronchodilator Reversibility Testing (if spirometry shows obstruction) 1

   • Perform in all children with FEV₁ <80% predicted or FEV₁/FVC <80%
   • Give 400 μg short-acting beta-agonist (SABA)
   • Positive test: ≥12% AND ≥200 mL increase in FEV₁
   • Important: Negative BDR does NOT exclude asthma 1

3. FeNO (Fractional Exhaled Nitric Oxide) 1

   • Recommended as first-line test alongside spirometry
   • UK NICE guidelines require two positive objective tests to confirm diagnosis 1

Step 3: Interpretation Strategy

The guidelines recommend AGAINST single abnormal test diagnosis. 1 You need:

• Multiple positive objective tests to confirm asthma
• Consider the pattern: children with probable asthma (high clinical suspicion but negative BDR/BHR) show intermediate lung function abnormalities between definite asthma and non-asthma 2

What NOT to Do

Never Use These Approaches Alone:

1. Trial of preventer medication alone (conditional recommendation against) 1

   • No evidence supports this approach
   • Can only be considered in symptomatic children with abnormal spirometry AND negative BDR, then repeat objective tests after 4-8 weeks 1

2. Symptom improvement after treatment to confirm diagnosis 1

   • This is widely used in practice but explicitly not recommended by guidelines

Comparison of Major Guidelines

The evidence shows some variation in approaches 1:

• GINA 2020: Spirometry + BDR or 2 weeks of peak flow variability
• BTS/SIGN 2019: Clinical diagnosis with lung function tests comparing symptomatic vs. asymptomatic periods
• UK NICE 2017: Requires two positive objective tests (spirometry/BDR + FeNO)
• ERS 2021 (most recent): Combination of spirometry, BDR, and FeNO as first-line

Critical Pitfalls to Avoid

1. Misinterpreting wheeze: Parents often confuse stridor and rattles with wheeze; the term doesn't translate well across languages 1

2. Timing matters: Asthma tests show significant diurnal and day-to-day variation—performing tests during asymptomatic periods may reduce diagnostic sensitivity 3

3. Age-specific considerations: These recommendations apply to children 5-16 years old. Preschool children (<5 years) require different diagnostic approaches, as spirometry is often normal and clinical predictive indices are more useful 4, 5

4. False reassurance from normal tests: Both normal spirometry and negative BDR can occur in children with asthma—consider repeated testing or additional tests like bronchial challenge 1, 2

Practical Implementation

For children with high clinical suspicion but initial negative tests 2:

• Monitor closely with repeated pulmonary function tests
• Look for subtle lung function impairments (FEF₂₅₋₇₅, FEF₇₅)
• Utilize allergic screening and FeNO
• Consider that 16-32% of children fall into "probable asthma" category with intermediate findings 6

The evidence strongly supports that children with ≥2 positive objective tests have more acute events and greater treatment benefit, but improvement can also occur in those with <2 positive tests, emphasizing the need for comprehensive assessment rather than rigid cutoffs. 6