To establish the impact of bronchodilator responsiveness (BDR) classification changes following the 2021 ERS-ATS technical statement, and to identify characteristics of patients in whom reclassification has occurred.

A convenience sample of six months of pulmonary function tests from a community-based specialist centre was analysed. Demographic, physical, prebronchodilator, and postbronchodilator characteristics were identified and tests of statistical significance performed.

921 tests were conducted. For FEV1, 91 tests were BDR according to 2005 criteria. 37 (41%) were reclassified in 2021, with 21 newly classified and 16 losing this classification. For FVC, 48 tests were BDR according to 2005 criteria. 18 (38%) were reclassified in 2021, with 14 newly classified and 4 losing this classification.

People with reclassified tests were significantly taller (mean 170.0 vs. 165.9 cm, p < 0.05) and heavier (mean 82.7 vs. 74.8 kg, p < 0.05), with larger prebronchodilator FEV1 (mean 2,216 vs 1,788 mL, p < 0.05) and FVC (mean 3457 vs 3045 mL, p=0.052), and had smaller relative changes in FEV1 (mean 12.1% vs 18.2%, p < 0.05) and FVC (mean 5.4% vs 12.7%). There were no significant differences in absolute postbronchodilator changes in FEV1 or FVC.

A large proportion of tests were reclassified, with more bronchodilator responsiveness based on the 2021 criteria. Reclassified tests had significantly larger lung volumes and smaller relative postbronchodilator changes.The large proportion of reclassified tests emphasises the importance of understanding procedural impacts causing variation in results, and clinical correlation based on the criteria of the day