Significant bronchodilator response in FEF25-75 for the diagnosis of asthma in children

Introduction: A spirometry with a significant bronchodilator response (SBDR) in FEV1, a methacholine concentration that produces a 20% drop in FEV1(PC20) ≤ 2 mg/ml and a positive exercise test (ET), have high specificity for the diagnosis of asthma in children. The value of FEF25-75 in spirometry has been questioned. The objective of this study was to relate SBDR in FEF25-75 of spirometry with normal FEV1 and FEV1/FVC, with bronchial hyperresponsiveness (BHR) to methacholine or exercise in children aged 5 to 15 years with clinical suspicion of asthma. Material and method: Cross-sectional study of spirometries performed between January 2017 and December 2019 in children aged 5-15 years with suspected asthma, who had a methacholine and/or exercise test within a period not exceeding 60 days. It was analyzed using STATA 14-0 and Microsoft Excel 2016 applying Chi-square tests. Results: The average age was 9.04 years (range: 5 – 14 years), 56.17% male. Of 324 spirometries with normal FEV1 and FEV1/FVC, 66 (20.4%) presented SBDR at FEF25-75. 47% and 33.3% of the children with and without RSB in FEF25-75, respectively, had PC20 ≤ 2 mg/ml and/or positive TE (p = 0.0396). Conclusions: children with suspected asthma and normal spirometry, with SBR in FEF25-75, had greater BHR than those without SBDR in FEF25-75. The SBDR in FEF25-75 was not always accompanied by an BHR that can confirm the diagnosis of asthma with high probability.