CHRONIC OBSTRUCTIVE PULMONARY DISEASE

Using the lower limit of normal for the FEV₁/FVC ratio reduces the misclassification of airway obstruction

M P Swanney¹, G Ruppel², P L Enright³, O F Pedersen⁴, R O Crapo⁵, M R Miller⁶, R L Jensen⁵, E Falaschetti⁷, J P Schouten⁸, J L Hankinson⁹, J Stocks¹⁰, P H Quanjer¹¹

¹ Respiratory Physiology Laboratory, Christchurch Hospital, Canterbury District Health Board, Christchurch, New Zealand
² Pulmonary Function Laboratory, St Louis University Hospital, St Louis, Missouri, USA
³ College of Public Health, The University of Arizona, Tucson, Arizona, USA
⁴ Institute of Public Health, Aarhus University, Aarhus, Denmark
⁵ Pulmonary Division, LDS Hospital and University of Utah, Salt Lake City, Utah, USA
⁶ Department of Medicine, University Hospital Birmingham NHS Trust, Birmingham, UK
⁷ Department of Epidemiology and Public Health, University College London, London, UK
⁸ Department of Epidemiology, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands
⁹ Valdosta, Georgia, USA
¹⁰ Portex Anaesthesia, Intensive Therapy and Respiratory Unit, UCL, Institute of Child Health, London, UK
¹¹ Department of Pulmonary Diseases, Erasmus Medical Centre, Erasmus University, Rotterdam, The Netherlands

Dr M P Swanney, Respiratory Physiology Laboratory, 4th Floor Riverside Building, Christchurch Hospital, Private Bag 4710, Christchurch 8140, New Zealand; maureen.swanney{at}cdhb.govt.nz

Aim: The prevalence of airway obstruction varies widely with the definition used.

Objectives: To study differences in the prevalence of airway obstruction when applying four international guidelines to three population samples using four regression equations.

Methods: We collected predicted values for forced expiratory volume in 1 s/forced vital capacity (FEV₁/FVC) and its lower limit of normal (LLN) from the literature. FEV₁/FVC from 40 646 adults (including 13 136 asymptomatic never smokers) aged 17–90+years were available from American, English and Dutch population based surveys. The prevalence of airway obstruction was determined by the LLN for FEV₁/FVC, and by using the Global Initiative for Chronic Obstructive Lung Disease (GOLD), American Thoracic Society/European Respiratory Society (ATS/ERS) or British Thoracic Society (BTS) guidelines, initially in the healthy subgroup and then in the entire population.

Results: The LLN for FEV₁/FVC varied between prediction equations (57 available for men and 55 for women), and demonstrated marked negative age dependency. Median age at which the LLN fell below 0.70 in healthy subjects was 42 and 48 years in men and women, respectively. When applying the reference equations (Health Survey for England 1995–1996, National Health and Nutrition Examination Survey (NHANES) III, European Community for Coal and Steel (ECCS)/ERS and a Dutch population study) to the selected population samples, the prevalence of airway obstruction in healthy never smokers aged over 60 years varied for each guideline: 17–45% of men and 7–26% of women for GOLD; 0–18% of men and 0–16% of women for ATS/ERS; and 0–9% of men and 0–11% of women for BTS. GOLD guidelines caused false positive rates of up to 60% when applied to entire populations.

Conclusions: Airway obstruction should be defined by FEV₁/FVC and FEV₁ being below the LLN using appropriate reference equations.

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