BACKGROUND: Spirometry tests with a bronchodilator response (BDR) in FEV1, a methacholine concentration that produces a 20% drop in FEV1 (PC20) ≤ 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 (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 spirometry 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 = .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.