Concordance between FVC and FEV6 for identifying chronic airflow obstruction and spirometric restriction in the Burden of Obstructive Lung Disease (BOLD) study

Abstract

Introduction We investigated whether the forced expiratory volume in 6 s (FEV6) can be used as a surrogate for the forced vital capacity (FVC). Methods The Burden of Obstructive Lung Disease is a multinational cohort study. At baseline, data were collected from adults, aged 40 years or older, from 41 sites across 34 countries. Participants from 18 sites were followed-up after a median of 8.3 years. Participants who completed the study core questionnaire and had acceptable post-bronchodilator spirometry were included. We performed receiver operating characteristic analyses to measure the ability of FEV1/FEV6 less than the lower limit of normal (LLN) to correctly classify FEV1/FVC less than the LLN, and FEV6 less than the LLN to correctly classify FVC less than the LLN. We used multilevel regression analyses to assess the association of discordant measurements with respiratory symptoms, quality of life and lung function decline. Results At baseline, 28 604 participants were included. 53% were female (15 060). 10% (2876) had chronic airflow obstruction for FEV1/FVC, compared with 9% (2704) for FEV1/FEV6. 37% (10 637) had spirometric restriction for FVC, compared with 35% (9978) for FEV6. The FEV1/FEV6 had excellent accuracy in identifying FEV1/FVC less than the LLN (area under the curve (AUC): 0.90, 95% CI, 0.89 to 0.91, κ coefficient 0.82). The FEV6 also had excellent agreement in identifying FVC less than the LLN (AUC: 0.95, 95% CI, 0.94 to 0.95, κ coefficient 0.90). Discordant reductions in FEV1/FEV6 (1%, 345) and FEV6 (1%, 309) were associated with greater odds of having respiratory symptoms and a lower physical quality of life. 3870 participants were followed up. Those with discordant reductions in FEV1/FEV6 and FEV6 were more likely to have chronic airflow obstruction and spirometric restriction at follow-up. Conclusions There is strong agreement between the FVC and FEV6 in the identification of chronic airflow obstruction and spirometric restriction.