Bronchodilator Response in [FEF.sub.25-75] for the Diagnosis of Asthma in Children

BACKGROUND: Spirometry tests with a bronchodilator response (BDR) in [FEV.sub.1], a methacho-line concentration that produces a 20% drop in [FEV.sub.1] ([PC.sub.20]) [less than or equal to] 2 mg/mL, and a positive exercise 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 ([FEF.sub.25-75]) in spirometry has been questioned. The objective of this study was to relate the BDR in [FEF.sub.25-75] of spirometry tests with normal [FEV.sub.1] and [FEV.sub.1]/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 ([+ or -] SD) age of the children was 9.04 [+ or -] 2.67 y, with a range of 5-15 y, and 56.17% were male. Of the 324 spirometry tests with normal [FEV.sub.1] and [FEV.sub.1]/FVC, 66 (20.4%) tests showed BDR in [FEF.sub.25-75]. A total of 46.9% and 33.3% of the children with and without BDR in [FEF.sub.25-75], respectively, had a [PC.sub.20] value [less than or equal to] 2 mg/mL and/or a positive exercise testing (P 5 .039). CONCLUSIONS: Children with suspected asthma and normal spirometry, other than BDR in [FEF.sub.25-75], had greater AHR than those without BDR in [FEF.sub.25-75]. BDR in [FEF.sub.25-75] was not always accompanied by AHR to confirm the diagnosis of asthma, so this study suggests that assessment of [FEF.sub.25-75] 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. Key words: spirometry; asthma; bronchial hyper-responsiveness; methacholine; exercise test; child; bronchodilator.