Diagnosing Childhood Asthma

Introduction to Diagnosis

• The European Respiratory Society recommends that the diagnosis of childhood asthma requires objective testing with spirometry, bronchodilator reversibility (BDR), and fractional exhaled nitric oxide (FeNO) as first-line tests, with at least two abnormal test results needed to confirm the diagnosis 1

Clinical Assessment

• Evaluate for key symptoms, particularly wheeze, which has better sensitivity (55-86%) and specificity (64-90%) for asthma diagnosis compared to other symptoms 2, 3
• Note that cough and breathing difficulty are nonspecific symptoms and should not be used alone to diagnose asthma 2
• Document symptom patterns, including frequency, triggers, and response to previous treatments 3

First-Line Objective Testing

• Spirometry testing measures FEV1 and FEV1/FVC ratio, with abnormal results indicating FEV1 or FEV1/FVC less than lower limit of normal (LLN) and/or <80% predicted 1
• Normal spirometry does not exclude asthma, and abnormal spirometry alone does not confirm it 1, 4
• Bronchodilator reversibility (BDR) testing should be performed even with normal spirometry if there is strong clinical suspicion, and a positive BDR indicates reversible airflow obstruction characteristic of asthma 1, 5
• Fractional exhaled nitric oxide (FeNO) testing should be performed before spirometry, with a cut-off of 25 ppb recommended, and elevated levels suggesting eosinophilic airway inflammation 1, 6

Additional Testing When Diagnosis Remains Unclear

• Peak expiratory flow rate (PEFR) variability can be considered, with 2 weeks of twice-daily PEFR measurements, and variability >12% suggesting asthma 1, 7

Diagnostic Decision Making

• Confirm diagnosis when at least two objective test results are abnormal, such as abnormal spirometry plus positive BDR or elevated FeNO 1, 4
• Consider watchful waiting when initial tests are normal but clinical suspicion remains high, and repeat testing when the child is symptomatic 1, 4

Important Caveats and Pitfalls

• Do not rely solely on symptoms for diagnosis, as using symptoms alone results in misdiagnosis in many children 2, 5
• Avoid diagnosis based only on treatment response, and do not diagnose asthma based solely on improvement in symptoms after a trial of preventer medication 5, 7, 8
• Consider age-appropriate approaches, with the ERS guidelines focusing on children aged 5-16 years 1, 2

Diagnosis of Asthma in Adolescents Using Objective Testing

Diagnostic Criteria

• In adolescents (≈ 15 years old), asthma can be confirmed when spirometry shows reversible small‑airway obstruction, even if allergy testing is negative. European Respiratory Society guideline. [9][10]
• The European Respiratory Society recommends that the presence of characteristic symptoms—recurrent bronchoconstriction and episodes of dyspnea (“unable to take a full breath”)—constitutes a clinical component of asthma diagnosis in children aged 5–16 years. [9][10]
• A positive bronchodilator reversibility test (significant improvement in airflow after bronchodilator administration) provides the second required abnormal objective test for asthma diagnosis according to ERS guidelines. [9][10]

Role of Allergy Testing

• The European Respiratory Society states that allergy testing (skin‑prick, total IgE) should not be used to diagnose asthma because of its low specificity; it may be employed only to identify potential triggers. [9][10]

Diagnostic Criteria and Confirmation of Asthma

Objective Lung‑Function Testing

• Spirometry that shows reversible small‑airway obstruction is the essential objective evidence for diagnosing asthma in children aged 5–16 years, as recommended by the European Respiratory Society (ERS) guideline (strong recommendation) 11.
• The ERS guideline states that the presence of any two abnormal objective tests—for example, abnormal spirometry together with a positive bronchodilator reversibility test—is sufficient to confirm an asthma diagnosis (strong recommendation) 11.

Clinical Presentation

• Recurrent episodes of bronchoconstriction constitute the characteristic clinical pattern of asthma, according to the American Family Physician review (expert opinion) 12.

Role of Allergy Testing

• The ERS guideline advises against using allergy (skin‑prick or IgE) tests to diagnose asthma because of their low specificity; however, these tests are valuable for phenotyping after a diagnosis has been established (moderate recommendation) [11][13].
• A negative allergy test should not lead to dismissal of an asthma diagnosis; the diagnosis must be based on objective lung‑function findings rather than atopy status (strong recommendation) 11.

European Respiratory Society Guidelines for Asthma Diagnosis in Children (5‑16 years)

Diagnostic Thresholds

• PEFR variability ≥ 12 % over a 2‑week period (twice‑daily morning and evening readings) is the diagnostic cut‑off for asthma in children aged 5‑16 years. 14
• The ≥ 12 % PEFR variability threshold applies uniformly across the entire 5‑16 year age range; the ERS guidelines do not stratify by narrower age groups. 15
• For spirometry, a bronchodilator response is considered diagnostic when FEV₁ increases by ≥ 12 % and/or ≥ 200 mL from baseline. 16
• A FeNO level of ≥ 25 ppb supports an asthma diagnosis when spirometry is normal. 16

Recommended Testing Sequence

• First‑line: Perform spirometry; an abnormal result is defined as FEV₁ or FEV₁/FVC < 80 % of predicted or below the lower limit of normal. 14
• If spirometry is abnormal: Conduct bronchodilator reversibility testing using FEV₁ with the ≥ 12 % and/or ≥ 200 mL threshold. 16
• If spirometry is normal: Measure FeNO; a value ≥ 25 ppb adds diagnostic weight. 16
• Only when the above tests are inconclusive: Use a 2‑week PEFR variability assessment, applying the ≥ 12 % cut‑off. 15

Role and Limitations of PEFR

• PEFR variability testing should be considered only after first‑line tests (spirometry with bronchodilator reversibility and FeNO) fail to confirm the diagnosis, or when bronchial challenge testing is unavailable. 14
• PEFR variability is regarded as an inferior diagnostic tool compared with direct bronchial challenge testing. 15
• PEFR should not be used alone for asthma diagnosis because its diagnostic accuracy is lower than that of spirometry‑based bronchodilator testing. 14
• The ≥ 12 % PEFR threshold refers to variability over two weeks, not to an acute post‑bronchodilator change; conflating the two leads to misinterpretation. 15

Test Performance Characteristics

• A negative bronchodilator test does not exclude asthma; clinicians should consider repeat or alternative testing during symptomatic periods. 16

Overall Diagnostic Requirement

• The ERS strongly recommends that at least two abnormal objective tests are required to confirm an asthma diagnosis in children. 14