Difficulties identifying and targeting COPD and population-attributable risk of smoking for COPD: a population study.

STUDY
OBJECTIVES: Respiratory public health interventions depend on accurate identification of the target group, yet this may vary depending on the diagnostic criteria used. We therefore compared the relative performance of various international criteria in identifying COPD cases. The burden of COPD due to smoking can only be determined from population-attributable risk (PAR) studies. These studies, lacking in the COPD literature, are necessary research in support of public health initiatives for COPD. In this representative population study, we also assessed the PAR for current and ex-smokers.
DESIGN: A representative biomedical population sample of 2,501 South Australians aged > or = 18 years (The Northwest Adelaide Health [Cohort] Study). COPD diagnosis and severity were determined according to various FEV1/FVC and FEV1 percentage of predicted criteria recommended by international respiratory authorities. Demographic, health behavior, and quality-of-life data were obtained by telephone interview and self-completed questionnaire.
SETTING: Northwest Adelaide. MEASUREMENTS AND
RESULTS: The PAR of smoking (smokers and ex-smokers) for COPD ranged from 51 to 70% depending on the diagnostic respiratory criteria used. COPD prevalence varied depending on the criteria used: American Thoracic Society, 5.4%; British Thoracic Society, 3.5%; European Respiratory Society (ERS), 5.0%; Global Initiative for Chronic Obstructive Lung Disease, 5.4%. There was also substantial disagreement in the cases identified. An alternative approach using ERS reference values one residual SD from the mean produced a COPD prevalence estimate of 6.9%, with improved level of agreement with the established respiratory criteria suggesting their potential as screening criteria.
CONCLUSIONS: The COPD risks associated with smoking and ex-smoking history were quantifiable using PAR, but PAR also suggests other, yet unquantified, risks. Targeting COPD cases for public health interventions is difficult given the range of spirometry criteria and the associated high level of underdiagnosis.