Potential misclassification of causes of death from COPD in a Danish population study

¹ Dept of Cardiology and Respiratory Medicine, Hvidovre Hospital, Hvidovre, Denmark
² Dept of Cardiology and Respiratory Medicine, Hvidovre Hospital, Hvidovre, Denmark; and The Copenhagen City Heart Study, Bispebjerg Hospital, Copenhagen, Denmark
³ Dept of Cardiology and Respiratory Medicine, Hvidovre Hospital, Hvidovre, Denmark; and North West Lung Centre, Wythenshawe Hospital, Manchester, UK

^* To whom correspondence should be addressed. E-mail: joergen.vestbo{at}hh.hosp.dk.

	Abstract

Little is known about causes of death in COPD and the validity of mortality statistics in COPD. We examined causes of death in the Copenhagen City Heart Study.

Of the 12,979 subjects with sufficient data from the baseline examination in 1976-78, 6,709 died before 2001. Of these, 242 died with COPD as cause of death. Among subjects with at least severe COPD at baseline only 24.9% had COPD as cause of death and in almost half of the cases where COPD was listed as cause of death the subject had a normal FEV₁/FVC ratio at baseline. In COPD patients, having COPD on the death certificate was associated with chronic mucus hypersecretion (CMH) at baseline, odds ratio (OR) 3.6 (95% confidence interval 1.7-7.7), and being female, OR 2.7 (1.3-5.6). In subjects without COPD, CMH and smoking predicted COPD as underlying cause of death, OR's 2.3 (1.5-3.7) and 2.2 (1.4-3.6), respectively.

We conclude that COPD is underreported on death certificates, that biases in the use of COPD as cause of death can be assessed, and that possible "over-diagnosis" of COPD on death certificates in subjects unlikely to have significant disease should make us cautious when using causes of mortality in COPD epidemiology.

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