Prevalence and predictors of undiagnosed chronic obstructive pulmonary disease in a Norwegian adult general population.

OBJECTIVES

To determine the prevalence and predictors of undiagnosed chronic obstructive pulmonary disease (COPD) in Norway.

METHODS

An age and gender stratified random sample of all adults aged 47-48 and 71-73 years in Bergen, Norway, were invited. The 3506 participants filled in questionnaires including symptoms of COPD, smoking, socio-economic status, self-rated health and cardiac co-morbidity. Spirometry was performed before and after inhalation of 400 microg of salbutamol. COPD was defined as post-bronchodilator forced expiratory volume in 1 s (FEV1) / forced vital capacity (FVC) < 0.7 whereas diagnosed COPD was defined as having received treatment for obstructive lung disease the last year.

RESULTS

Three hundred-three persons (9%) were classified as having COPD, and the undiagnosed fraction was 66%. In multiple logistic regression analysis, including multiple imputation, predictors of undiagnosed COPD were absence of COPD symptoms [odds ratio (OR) 6.92, P = 0.001], and self-report of being in good/excellent health (OR 2.39, P = 0.005). When post-bronchodilator FEV1 was added to the analysis, undiagnosed disease was predicted by pack years [OR 1.21 (1.01-1.47) per 10 pack-year increase, P = 0.043], and close to normal lung function [OR 1.48 (1.22-1.80) per 10% increase in post-bronchodilator FEV1 % predicted, P < 0.001]. Anthropometrical variables, socio-economic status and cardiac co-morbidity were not associated with having undiagnosed COPD.

CONCLUSION

Two out of three COPD patients in Norway are undiagnosed. Risk factors for being undiagnosed are moderate reduction in lung function, absence of COPD symptoms and self-report of being in good health.