Should we use FEV1/FVC <0.70 or FEV1/FVC <LLN to identify subjects with a clinical history indicating COPD – Results from the population-based BOLD study in Salzburg, Austria

Rationale: To compare the fixed ratio of 0.70 and the LLN to identify subjects presenting with a clinical history indicating COPD. Methods: We used data from the population-based Austrian Burden of Obstructive Lung Disease (BOLD) study. Participants were aged >= 40 years and completed post-bronchodilator spirometry. Risk factors for COPD and respiratory symptoms were recorded. A clinical history indicating COPD was defined as the presence of one or more risk factors and any concomitant respiratory symptom(s). Results: Among 1258 participants 255 (20.3%) reported presence of one or more risk factors and presence of one or more respiratory symptoms, and were therefore considered to present with a clinical history indicating COPD. Among those the proportion of airways obstruction defined by FEV1/FVC<LLN and FEV1/FVC<0.70 was 26% and 39%, respectively. Altogether 99 (7.9%) subjects presented with a clinical history indicating COPD and FEV1/FVC<0.70, while 65 (5.2%) presented with a clinical history indicating COPD and FEV1/FVC <LLN. 62% of 34 participants with a clinical history indicating COPD and discordant results for airways obstruction (FEV1/FVC<0.70 but FEV1/FVC >LLN) demonstrated FEV1 >80% predicted, and would be considered to have mild disease (GOLD stage 1). Conclusion: Utilization of the LLN as a threshold for the FEV1/FVC ratio would identify approximately two thirds of subjects with a clinical history indicating COPD and GOLD-defined airways obstruction. The majority of those not identified when using the LLN would have mild disease (GOLD stage I).