R e s pi r a t o r y e p i d em i o l o g y Table 1 Demographics and baseline characteristics of 10 360 participants with usable spirometry data N Age (years) Current smoker, % Cigarette exposure Pack-years (full cohort) Pack-years (ever smokers) BMI (kg/m2) Pre-BD FEV1, % pred Post-BD FEV1, % pred GOLD stages* Stage 1, % Stage 2, % Stage 3, % Stage 4, % Any respiratory medication, % Asthma ever, % 558 59.0 (12.4) 14.3 12.4 (25.4) 24.6 (31.3) 28.0 (5.1) 93.3 (18.1) 95.9 (17.3) 8.3 9.3 1.3 0.0 23.0 17.2 1298 57.7 (11.6) 19.2 13.2 (20.9) 25.3 (23.1) 26.4 (4.2) 92.8 (17.5) 95.5 (16.7) 14.8 8.3 1.1 0.1 6.4 7.1 845 56.1 (11.9) 13.5 11.9 (23.4) 22.7 (29.1) 26.7 (5.2) 95.6 (18.4) 99.2 (17.9) 10.2 6.3 0.7 0.2 32.4 14.3 572 704 54.0 58.2 (10.9) (11.0) 28.2 20.6 11.1 15.1 (17.9) (20.9) 26.8 25.1 (18.8) (21.9) 23.2 27.3 (3.4) (4.6) 84.8 95.2 (14.8) (17.5) 86.5 97.5 (14.5) (16.9) 4.3 5.6 1.5 0.2 2.6 3.2 8.1 5.6 0.7 0.2 19.7 9.7 760 56.4 (11.8) 18.3 12.8 (24.9) 21.0 (29.1) 27.9 (4.9) 89.8 (16.4) 93.0 (16.0) 8.6 6.7 1.6 0.3 30.0 16.7 517 56.7 (9.9) 26.3 23.4 (29.3) 38.6 (28.9) 30.7 (6.9) 83.4 (18.8) 86.7 (18.2) 5.4 10.7 3.7 0.2 44.0 22.1 676 60.1 (12.8) 26.0 12.7 (16.5) 20.1 (16.7) 26.5 (4.3) 92.3 (16.7) 94.7 (16.5) 11.9 7.7 0.9 0.5 13.8 17.3 916 52.3 (10.3) 32.4 9.7 (17.1) 18.5 (19.8) 24.8 (4.7) 74.7 (15.4) 77.0 (15.1) 1.2 7.1 3.7 0.7 26.5 6.6 562 55.8 (11.6) 28.8 16.1 (25.3) 26.3 (28.0) 27.6 (4.7) 92.2 (18.3) 94.9 (17.8) 11.6 8.6 1.8 0.0 8.6 7.3 865 54.2 (10.4) 45.9 11.5 (16.3) 17.0 (17.4) 27.8 (7.4) 76.8 (19.5) 79.4 (19.0) 4.0 13.0 5.8 0.6 9.8 14.7 553 58.4 (11.0) 14.7 10.5 (16.2) 18.3 (17.7) 27.0 (4.4) 93.0 (16.1) 95.8 (16.1) 9.6 4.7 1.5 0.0 41.6 14.5 846 53.7 (10.6) 33.7 16.0 (27.0) 29.6 (30.8) 29.5 (5.5) 89.0 (18.5) 92.3 (17.7) 8.6 9.1 1.1 0.4 6.0 6.4 688 58.2 (11.5) 21.1 16.3 (31.8) 26.3 (36.9) 27.1 (5.0) 87.6 (17.9) 90.7 (17.3) 11.0 9.3 2.1 0.2 22.5 19.5 DFEV1 (ml) and DFVC (ml) are absolute change after bronchodilator; DFEV1i and DFVCi are change as a per cent of initial value. DFEV1p and DFVCp are change as per cent of predicted value. N1 is number with non-missing FEV1 values and N2 is number with non-missing FVC values. COPD GS2+ ¼ FEV1/FVC <0.7 and FEV1% predicted<80%; COPD GS2+ (without asthma) ¼ post-bronchodilator spirometrically deﬁned COPD excluding those with self-reported asthma. COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity. Thorax 2012;67:718e726. doi:10.1136/thoraxjnl-2011-201445 Variables FEV1-based measures DFEV1 (ml) DFEV1i (%) DFEV1p (%) FVC-based measures DFVC (ml) DFVCi (%) DFVCp (%) 720 Australia Austria Canada China Germany Iceland Kentucky South Norway Philippines Poland Africa Sweden Turkey UK Continuous data presented as mean (SD) unless otherwise stated. *GOLD stage I: FEV1/FVC<70% and FEV1$80% predicted; GOLD stage II: FEV1/FVC<70% and 50%#FEV1<80% predicted; GOLD stage III: FEV1/FVC<70% and 30%#FEV1<50% predicted; GOLD stage IV: FEV1/FVC<70% and FEV1<30% predicted. BMI, body mass index; FEV1, forced expiratory volume in 1 s; GOLD, Global Initiative for Chronic Obstructive Lung Disease; FVC, forced vital capacity; Pre-BD FEV1 % pred, pre-bronchodilator FEV1 % predicted; Post-BD FEV1 % pred, post-bronchodilator FEV1 % predicted. thresholds. The proportion of people in the COPD subgroups who exceeded the FEV1-based thresholds (except for DFEV1i) decreased with increasing severity of COPD as deﬁned by GOLD stages.24 By contrast, the proportion of people in the COPD subgroups who exceeded the FVC-based thresholds showed a tendency to increase with severity. DISCUSSION We measured the BDR in general population samples, aged 40 and older, from sites in 14 countries spanning four continents. The main ﬁndings indicated that the thresholds or upper limit of normality for the per cent change in FEV1 relative to initial level is 12% and for the FEV1 relative to predicted FEV1 is 10% without heterogeneity across populations. These values agree well with current ATS guideline cutoffs for deﬁning a signiﬁcant BDR and strengthen the applicability of these measures for global interpretation in bronchodilator testing. We further vali- dated these thresholds in people with and without obstruction and conﬁrmed that a higher proportion of people with obstruction of all stages of severity had BDR compared with those without obstruction, ﬁndings that are consistent with previous studies in healthy individuals and people with airway obstruction using ATS-ERS thresholds.10 There were two secondary ﬁndings. First, the BDR threshold for people with chronic airﬂow obstruction was lower when asthma was excluded, but there was considerable overlap between the two groups with and without exclusion of asthma, consistent with previous studies.1 26 27 Also, there were differ- ences between the FEV1-based and the FVC-based thresholds in their association with severity of airﬂow obstruction. The proportion with reversibility measured by changes in FEV1 generally decreased as COPD severity increased while that with reversibility measured by changes in FVC increased with increasing COPD severity, ﬁndings which are consistent Table 2 Mean and SD (unweighted values) for bronchodilator responses for whole study population, healthy and COPD subgroups Study population All N1¼10 217 82 (139) 3.7 (6.9) 2.8 (4.8) N2¼9546 0 (237) 0.5 (7.9) 0.1 (6.6) Men N1¼4826 95 (156) 3.6 (6.5) 2.7 (4.6) N2¼4560 4 (257) 0.5 (6.9) 0.2 (5.9) Women N1¼5391 70 (120) 3.8 (7.3) 2.8 (5.0) N2¼4986 4 (217) 0.5 (8.7) 0 (7.3) Healthy subgroup Men and women COPD GS2+ Men and women N1¼3922 72 (130) 3.1 (6.0) 2.6 (4.8) N2¼3593 21 (219) 0.3 (7.4) 0.5 (6.7) N1¼1009 114 (157) 8.8 (11.9) 4.2 (5.7) N2¼976 153 (280) 6.9 (12.2) 4.4 (7.9) COPD GS2+ (without asthma) Men and women N1¼745 104 (153) 7.7 (11.0) 3.7 (5.5) N2¼723 138 (273) 6.2 (11.9) 4.0 (7.6)