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13-09-2009 | Respiratory | Article

Fixed-ratio criterion overestimates COPD prevalence

Abstract

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MedWire News: Using a fixed cutoff with the FEV1/FVC ratio to diagnose chronic obstructive pulmonary disease (COPD) overestimates the burden of disease, especially in older individuals, researchers have shown.

Instead, they recommend applying the lower limit of normal (LLN) criterion to the FEV1/FVC ratio in order to minimize age bias and better reflect the presence of clinically significant irreversible airflow limitation.

The conclusions come from the Burden of Obstructive Lung Disease (BOLD) Collaborative Research Group, who compared various spirometric COPD definitions in a population-based sample of 10,001 adults aged ≥40 years.

The definitions they studied included the fixed-ratio criterion (post-bronchodilator FEV1/FVC <0.70) recommended by the Global Initiative for Chronic Obstructive Lung Disease (GOLD), the GOLD stages 2–4 definition (FEV1/FVC <0.70 and FEV1 <80% predicted), the LLN of the FEV1/FVC (ie, <5th percentile of FEV1/FVC), and the ratio of FEV1 to FEV6.

The prevalence of COPD was significantly higher when defined with the fixed-ratio criterion than with any of the other definitions, report William Vollmer (Center for Health Research, Portland, Oregon, USA) and co-authors in the European Respiratory Journal.

The fixed ratio estimates were generally 5–11% higher than those for GOLD stages 2–4, whereas the LLN (FEV1/FVC) criterion produced estimates that were intermediate between those obtained with the two GOLD-based definitions.

Importantly, the prevalence of COPD using the fixed-ratio criterion increased sharply with age, even among healthy never-smokers. By contrast, the other definitions produced estimates that increased only marginally with age. Finally, prevalence estimates were very similar when the FEV1/FEV6 ratio was used in place of the FEV1/FVC ratio.

“Adjusting the FEV1/FVC for normative aging effects appears to reduce the rate of false–positive diagnoses that has been reported for older individuals, and the added requirement of a low FEV1 further reduces the age-related increase in COPD prevalence seen among healthy never-smokers,” Vollmer’s team concludes.

They add: “Our study also supports the use of the FEV1/FEV6 as a practical substitute for the FEV1/FVC.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

By Joanna Lyford

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