Background: Little is known on the long term outcomes of individuals with mild COPD, as defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD).
Methods: A population cohort of 6671 randomly selected adults without asthma was stratified into categories of modified GOLD-defined COPD (pre-bronchodilator spirometry). Further stratification was based on the presence or absence of respiratory symptoms. After 11 years, associations between baseline categories of COPD and FEV1 decline, respiratory care utilization, and quality of life as measured by the SF-36 questionnaire, were examined after controlling for age, sex, smoking and educational status.
Results: At baseline, modified GOLD criteria were met by 610 (9.1%) participants from whom 519 (85.1%) had stage 1 COPD. At follow-up, individuals with symptomatic stage 1 COPD (n=224) had faster FEV1 decline (-9 ml/yr [CI95% -13; -5]), increased respiratory care utilization (OR 1.6 [CI95% 1.0 ; 2.6]) and lower quality of life compared to asymptomatic subjects with normal lung function (n=3627, reference group). By contrast, asymptomatic stage 1 COPD subjects (n=295) had no significant differences in FEV1 decline (-3 ml/yr [CI95% -7; +1]), respiratory care utilization (OR 1.05 [CI95% 0.63 ;1.73]) or quality of life scores when compared to the reference group.
Conclusions: In population-based studies, respiratory symptoms are of major importance for predicting long-term clinical outcomes in COPD subjects with mild obstruction. Population studies that are based on spirometry only may misestimate the prevalence of clinically relevant COPD.