Post-Bronchodilator PEFR Improvement for Asthma Diagnosis in a 6-Year-Old
A PEFR variability of ≥12% is the diagnostic threshold for asthma in children aged 5-16 years, including 6-year-olds, according to the European Respiratory Society guidelines. 1
Important Context: PEFR Is Not a First-Line Diagnostic Test
The European Respiratory Society explicitly recommends that PEFR variability testing should only be considered when first-line tests (spirometry with bronchodilator reversibility and FeNO) fail to confirm the diagnosis, or in healthcare settings where bronchial challenge testing is unavailable. 1 PEFR variability is considered an inferior choice compared to direct bronchial challenge testing. 1
Diagnostic Threshold and Measurement Protocol
The diagnostic cut-off is ≥12% variability in PEFR measurements over a 2-week period with twice-daily readings (morning and evening). 1, 2
This threshold applies across the entire pediatric age range of 5-16 years, as the ERS guidelines did not stratify recommendations by specific age groups within this range. 1
Critical Distinction: PEFR Variability vs. Bronchodilator Response
The question asks about post-bronchodilator PEFR improvement, but the evidence base focuses on PEFR variability over time, not immediate bronchodilator response. The ERS guidelines recommend:
For spirometry (FEV₁): A bronchodilator response of ≥12% AND/OR ≥200 mL is diagnostic. 1
For PEFR: The guidelines reference variability (≥12% over 2 weeks), not acute bronchodilator response. 1, 2
Research evidence shows that PEFR and FEV₁ do not correlate perfectly in bronchodilator response—43% of patients with significant FEV₁ changes (≥15%) showed PEFR changes <15%, and conversely, 33% with minimal FEV₁ changes had PEFR changes ≥15%. 3 This discrepancy makes immediate post-bronchodilator PEFR measurement unreliable as a standalone diagnostic tool.
Proper Diagnostic Algorithm for a 6-Year-Old
The ERS strongly recommends that asthma diagnosis requires at least two abnormal objective tests. 1, 2 The proper sequence is:
Perform spirometry first: Look for FEV₁ or FEV₁/FVC <80% predicted or below lower limit of normal. 1
If spirometry is abnormal: Perform bronchodilator reversibility testing with FEV₁ (not PEFR), using the ≥12% and/or ≥200 mL threshold. 1
If spirometry is normal: Measure FeNO (≥25 ppb supports asthma diagnosis). 1
Only if the above tests are inconclusive: Consider 2-week PEFR variability testing with the ≥12% threshold. 1, 2
Common Pitfalls to Avoid
Do not use PEFR alone for diagnosis: The ERS guidelines emphasize that no single test is sufficient, and PEFR has lower diagnostic accuracy than spirometry-based bronchodilator testing. 1, 2
Do not confuse acute bronchodilator response with variability: The 12% threshold for PEFR refers to variability over 2 weeks, not immediate post-bronchodilator change. 1
Recognize low sensitivity: Even the 12% threshold for FEV₁ bronchodilator response has only 28.7-35% sensitivity in children, though specificity is excellent at 90-98%. 1, 4 A negative test does not exclude asthma. 1, 2
Consider that spirometry may be normal when asymptomatic: In a well-controlled 6-year-old, spirometry and bronchodilator testing may be normal between episodes, necessitating repeat testing during symptomatic periods. 2, 5