What tests are used to diagnose asthma in children?

Diagnostic Testing for Asthma in Children

In children aged 5-16 years, diagnose asthma using a combination of objective tests—specifically spirometry, bronchodilator reversibility (BDR) testing, and fractional exhaled nitric oxide (FeNO)—with at least two abnormal results required to confirm the diagnosis; never diagnose based on symptoms alone. 1

First-Line Objective Tests (Ages 5-16 Years)

Spirometry

• Perform spirometry as the initial test in all children with suspected asthma (strong recommendation). 1
• Consider results abnormal when FEV₁ or FEV₁/FVC is less than the lower limit of normal (LLN) and/or <80% predicted. 1
• Normal spirometry does not exclude asthma—many children with asthma have normal baseline lung function. 1, 2
• Abnormal spirometry alone does not confirm asthma; additional testing is required. 1, 2

Bronchodilator Reversibility (BDR) Testing

• Perform BDR testing in all children with abnormal spirometry (FEV₁ <LLN or <80% predicted and/or FEV₁/FVC <LLN or <80%). 1
• Administer 400 μg of short-acting beta-agonist (SABA) and repeat spirometry. 1
• Consider BDR positive when FEV₁ increases ≥12% AND/OR ≥200 mL—this supports an asthma diagnosis. 1
• BDR testing can be performed even with normal baseline spirometry if clinical suspicion is high. 1, 2
• A negative BDR (<12% improvement) does not exclude asthma. 1

Fractional Exhaled Nitric Oxide (FeNO)

• Measure FeNO as part of the diagnostic work-up (strong recommendation). 1
• Ideally perform FeNO before spirometry, though many clinics perform both tests together. 1
• A FeNO value ≥25 ppb in a symptomatic child supports an asthma diagnosis. 1, 2
• FeNO <25 ppb does not exclude asthma. 1
• Elevated FeNO suggests eosinophilic airway inflammation characteristic of asthma. 2

When Initial Tests Are Inconclusive

Peak Expiratory Flow Rate (PEFR) Variability

• Use PEFR variability only when other objective tests are unavailable (conditional recommendation against using as primary test). 1
• Obtain 2 weeks of twice-daily measurements, ideally using electronic peak flow meters. 1, 2
• PEFR variability ≥12% suggests asthma. 1, 2
• This is an inferior choice compared to bronchial challenge testing. 1

Bronchial Challenge Testing

• Perform direct challenge testing with methacholine or indirect challenge testing (exercise) when diagnosis remains unclear after initial testing. 1
• Methacholine challenge is FDA-approved for diagnosing bronchial airway hyperreactivity in patients 5 years and older who do not have clinically apparent asthma. 3
• A positive challenge test confirms airway hyperreactivity characteristic of asthma. 1

Diagnostic Algorithm

Confirm asthma diagnosis only when at least two objective test results are abnormal, such as: 1, 2

• Abnormal spirometry + positive BDR
• Abnormal spirometry + elevated FeNO (≥25 ppb)
• Positive BDR + elevated FeNO

Special Considerations for Young Children (<5 Years)

Children under 5-6 years cannot reliably perform spirometry, BDR testing, or FeNO measurements due to developmental limitations. 4

For this age group:

• Document recurrent wheeze as the most important symptom suggesting asthma. 4
• Use a therapeutic trial approach when objective testing is not feasible. 4
• Observe direct improvement with SABA (with or without oral corticosteroids) during an acute exacerbation by a trained healthcare practitioner (preferred method). 5
• Alternatively, assess parental report of symptomatic response to a 3-month trial of medium-dose inhaled corticosteroids with as-needed SABA. 5
• Consider the diagnosis in children 1-5 years with frequent symptoms (≥8 days/month) or recurrent exacerbations (≥2 episodes). 5

Critical Pitfalls to Avoid

Never Diagnose Based on Symptoms Alone

• The European Respiratory Society strongly recommends against diagnosing asthma based on symptoms alone (strong recommendation, moderate quality evidence). 1
• Recurrent wheeze has better diagnostic accuracy (sensitivity 55-86%, specificity 64-90%) than cough or breathing difficulty, which are nonspecific. 2
• Using symptoms alone results in misdiagnosis in a considerable number of children. 1, 2

Never Diagnose Based on Treatment Response Alone

• Do not diagnose asthma based solely on improvement in symptoms after a trial of preventer medication (conditional recommendation against). 1
• A trial of preventer medication can be considered only in symptomatic children with abnormal spirometry and negative BDR, with repeat objective testing after 4-8 weeks. 1

Do Not Use Allergy Testing for Diagnosis

• Allergy testing may help identify triggers but has low specificity for asthma diagnosis and should not be used as a diagnostic criterion. 4

Avoid Vague Labels

• Do not use terms like "bronchitis" or "reactive airway disease" as these delay proper diagnosis and treatment. 4

When to Refer

• Chronic cough (>4 weeks) as the only symptom—unlikely to be asthma; investigate according to chronic cough guidelines. 1
• When initial objective tests fail to confirm diagnosis despite high clinical suspicion, consider watchful waiting with repeat testing when symptomatic. 1, 2
• When diagnosis remains uncertain after comprehensive testing, refer for specialist evaluation. 1