Comparison of spirometry criteria for the diagnosis of COPD: results from the BOLD study

Abstract

Published guidelines recommend spirometry to accurately diagnose chronic obstructive pulmonary disease (COPD). However, even spirometry-based COPD prevalence estimates can vary widely. We compared properties of several spirometry-based COPD definitions using data from the international Burden of Obstructive Lung Disease (BOLD)study. 14 sites recruited population-based samples of adults aged > or =40 yrs. Procedures included standardised questionnaires and post-bronchodilator spirometry. 10,001 individuals provided usable data. Use of the lower limit of normal (LLN) forced expiratory volume in 1 s (FEV(1)) to forced vital capacity (FVC) ratio reduced the age-related increases in COPD prevalence that are seen among healthy never-smokers when using the fixed ratio criterion (FEV(1)/FVC <0.7) recommended by the Global Initiative for Chronic Obstructive Lung Disease. The added requirement of an FEV(1) either <80% predicted or below the LLN further reduced age-related increases and also led to the least site-to-site variability in prevalence estimates after adjusting for potential confounders. Use of the FEV(1)/FEV(6) ratio in place of the FEV(1)/FVC yielded similar prevalence estimates. Use of the FEV(1)/FVC<LLN criterion instead of the FEV(1)/FVC <0.7 should minimise known age biases and better reflect clinically significant irreversible airflow limitation. Our study also supports the use of the FEV(1)/FEV(6) as a practical substitute for the FEV(1)/FVC.

FIGURE 1

Comparison of chronic obstructive pulmonary disease (COPD) prevalence for various alternative definitions of COPD for participants in the Burden of Obstructive Lung Disease (BOLD) study. a) Contrasting prevalences for each definition within site. ■: fixed ratio; : lower limit of normal (LLN) (ratio); □: Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages 2–4; : LLN (ratio) and forced expiratory volume in 1 s (FEV1) <80% predicted; : LLN (ratio) and LLN (FEV1). b) Contrasting site differences within each definition. Significant site-to-site variability persisted for each of the estimates even after adjusting for age, sex, cigarette smoking (pack-yrs), body mass index, years worked in a dusty job and interactions of sex with both age and smoking history in logistic regression models (Wald statistics ranging from 7.1 to 8.6, all p-values <0.0001). Prevalences based on the fixed ratio are significantly higher than for all other estimators at each site (all p-values <0.001). : Guangzhou, China; : Adana, Turkey; : Salzburg, Austria; : Reykjavik, Iceland; : Cape Town, South Africa; □: Krakow, Poland; : Hanover, Germany; ■: Bergen, Norway; : Vancouver, BC, Canada; : Manila, Philippines; : Lexington, KY, USA; : Sydney, Australia; : London, UK; : Uppsala, Sweden.

FIGURE 2

Prevalence of “chronic obstructive pulmonary disease” among healthy never-smokers in the Burden of Obstructive Lung Disease (BOLD) study (data from all sites combined). Wald statistics for comparing the four age groups (and adjusted for site, sex, body mass index and years worked in a dusty job) ranged from 62.6 for the fixed ratio criterion, to 24.5 for Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages 2–4, to ~6.6 for the two analogues of these criteria in which the forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC) ratio <0.7 is replaced by FEV1/FVC

FIGURE 3

Prevalence of Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages 2–4 chronic obstructive pulmonary disease in the Burden of Obstructive Lung Disease (BOLD) study using the Third US National Health and Nutrition Examination Survey (NHANES-III) and site-specific prediction equations (data from all sites combined). Site differences were greater when using the NHANES-III equations (Wald statistic 9.5, p<0.0001) or Hordaland county equations (Wald statistic 8.4, p<0.0001) than when using the site-specific equations (Wald statistic 4.7, p<0.0001). The estimated prevalences were significantly higher (p<0.0001 for all age groups) when using common reference equations for all sites (NHANES-III and Hordaland County) than when using local prediction equations. The NHANES-III and Hordaland County prevalence estimates differed significantly overall and for the oldest age group. : NHANES-III; □: Hordaland County; Δ: local equations.