| Summary: | Abstract Background Possible variation in bronchodilator response (BDR) according to age at the diagnosis of adult-onset asthma is unknown. Our aim was to assess if BDR in FEV1 is related to age at diagnosis of adult-onset asthma and how many subjects fulfill the 400 mL criterion of BDR, the suggested cut-off for asthma-like reversibility in asthma-COPD overlap (ACO). Methods A total of 1030 patients with adult-onset asthma were included; 245 from SAAS (Seinäjoki Adult Asthma Study, Finland) and 785 from COREA (Cohort for Reality and Evolution of Adult Asthma in Korea) cohorts. BDR in FEV1 at the diagnosis of asthma was assessed. Patients were divided into groups based on age at asthma diagnosis: < 40, 40–59.9, and ≥ 60 years. The cohorts were analyzed separately. Results BDR % in FEV1 did not differ between the groups of different age at asthma diagnosis and no correlation between BDR and age was found. Of patients aged ≥40 years, only 18% (SAAS-cohort) and 5% (COREA-cohort) reached the 400 mL BDR in FEV1. After exclusion of possible ACO patients, the results remained similar. Conclusion By using two large cohorts of steroid-naive patients with asthma, we have shown that BDR at diagnosis of asthma is constant over large age span range, and the limit of 400 mL in BDR in FEV1 is rarely reached. Trial registration Seinäjoki Adult Asthma Study is registered at ClinicalTrials.gov with identifier number NCT02733016 .
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