Bronchodilator Response in FEF25-75 for the Diagnosis of Asthma in Children

BACKGROUND: Spirometry tests with a bronchodilator response (BDR) in FEV1, a methacho-line concentration that produces a 20% drop in FEV1 (PC20) <= 2 mg/mL, and a positive exer-cise test have high specificity for the diagnosis of asthma in children. However, the value of forced expiratory flow during the middle half of the FVC maneuver (FEF25-75) in spirometry has been questioned. The objective of this study was to relate the BDR in FEF25-75 of spirometry tests with normal FEV1 and FEV1/FVC to airway hyper-responsiveness (AHR) to methacholine or exercise in children age 5-15 y with clinical suspicion of asthma. METHODS: This was a cross-sectional study of spirometry tests performed between January 2017-December 2019 in children age 5-15 y with diagnostic suspicion of asthma who had a methacholine and/or exercise testing within a period not exceeding 60 d between exams. RESULTS: The mean (+/- SD) age of the children was 9.04 +/- 2.67 y, with a range of 5-15 y, and 56.17% were male. Of the 324 spi-rometry tests with normal FEV1 and FEV1/FVC, 66 (20.4%) tests showed BDR in FEF25-75. A total of 46.9% and 33.3% of the children with and without BDR in FEF25-75, respectively, had a PC20 value <= 2 mg/mL and/or a positive exercise testing (P 5 .039). CONCLUSIONS: Children with suspected asthma and normal spirometry, other than BDR in FEF25-75, had greater AHR than those without BDR in FEF25-75. BDR in FEF25-75 was not always accompanied by AHR to confirm the diagnosis of asthma, so this study suggests that assessment of FEF25-75 alone is not always reliable for ruling in or ruling out AHR in the setting of otherwise normal spirometry results in children with suspected asthma.