Abstract
Introduction: The post-bronchodilator ratio of FEV1 to vital capacity is used for defining airway obstruction in COPD, but the definition of this ratio varies between different guidelines. There are few studies determining the consequences of the choice between the different definitions.
Aim: To identify consequences of the choice between three criteria for airway obstruction:
1) FEV1/FVC<0.7
2) FEV1/MaxVC<0.7
3) FEV1/FVC<LLN
Method: These criteria were applied to a general population sample (N=4,024, ages 31-85 yy, 50.8% women) collected in 2002-2004 in Sweden. MaxVC was defined as the highest value of forced (FVC) and slow (SVC) vital capacity. Subjects with airway obstruction were stratified to GOLD grades 1-4 of airflow limitation. LLN was defined by the GLI reference values.
Result: The prevalence of COPD was 13.1%, 17.2% and 7.0% according to definition 1-3, respectively. Criterion 2 included all subjects identified by the other two criteria except for six subjects (0.6%, all 31-32 y) identified by LLN only. Subjects identified by LLN were significantly younger, mean age 63 years versus 66 years according to criteria 1 and 2, and had more respiratory symptoms such as cough and wheeze. They were also less likely to be never-smokers, i.e. 14.6% versus 22.1% (criterion 2) and 20.0% (criterion 1). Subjects identified by criterion 2 only had GOLD grades 1-4, i.e. not only mild to moderate airflow limitation but also more severe disease.
Conclusion: The various diagnostic criteria identify diverse groups. This should be considered in epidemiological studies, and can have important implications in a clinical setting.
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