Accuracy of national mortality codes in identifying adjudicated cardiovascular deaths

Objective: This study investigated the sensitivity and specificity of the national mortality codes in identifying cardiovascular disease (CVD) deaths and documents methods of verification. Methods: A 12-year retrospective case ascertainment of all ICD-coded CVD deaths was performed for deaths between 1990 and 2002 in the Melbourne Collaborative Cohort Study, comprising 41,528 subjects. Categories of non-CVD codes were also examined. Stratified samples of 750 deaths were adjudicated from a total of 2,230 deaths. Expert panels of cardiologists and neurologists adjudicated deaths. Results: Of the 750 deaths adjudicated, 582 were verified as CVD [392 coronary heart disease (CHD) and 92 stroke] and 168 non-CVD. Estimated sensitivity and specificity of national mortality codes for identifying specific causes of death were: CHD 74.2% (95% CI: 69.8-78.5%) and 97.6% (96.0-99.2%), respectively; myocardial infarction 59.9% (50.9-69.0%) and 94.2% (92.4-96.0%), respectively; haemorrhagic stroke 58.9% (46.0-71.7%) and 99.8% (99.4-100.0%), respectively and; ischaemic stroke 38.7% (20.5-56.9%) and 99.9% (99.6-100.0%), respectively. Misclassification was most common for deaths with primary ICD codes for endocrine-metabolic and genito-urinary diseases. Conclusions: National mortality coding under-estimated the true proportion of CHD and stroke deaths in the cohort by 13.6% and 50.8%, respectively. Implications: Misclassification of cause of death may have implications for conclusions drawn from epidemiological research.