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Accuracy of national mortality codes in identifying adjudicated cardiovascular deaths
Linton R Harriss1, Andrew E Ajani, David Hunt
1Department of Epidemiology and Preventive Medicine, Monash University, Victoria. linton.harriss@monash.edu
Insights
National mortality codes underestimated cardiovascular disease (CVD) deaths, particularly stroke. Accurate cause-of-death coding is crucial for reliable epidemiological research on heart disease and stroke.
Area of Science:
- Epidemiology
- Public Health
- Biostatistics
Background:
- Accurate cause-of-death (COD) assignment is essential for epidemiological research and public health surveillance.
- National mortality coding systems are widely used but their accuracy in identifying specific diseases like cardiovascular disease (CVD) requires validation.
Purpose of the Study:
- To evaluate the sensitivity and specificity of national mortality codes in identifying cardiovascular disease (CVD) deaths.
- To document the methods used for verifying the accuracy of CVD death classifications.
Main Methods:
- A 12-year retrospective analysis of deaths (1990-2002) within the Melbourne Collaborative Cohort Study (n=41,528).
- Expert panel adjudication of a stratified sample of 750 deaths to verify the accuracy of International Classification of Diseases (ICD) codes.
- Examination of non-CVD codes and misclassification patterns.
Main Results:
- Of 750 adjudicated deaths, 582 were verified as CVD (392 coronary heart disease [CHD], 92 stroke) and 168 as non-CVD.
- Estimated sensitivity for CHD was 74.2% and specificity 97.6%; for myocardial infarction, 59.9% and 94.2%, respectively.
- Estimated sensitivity for haemorrhagic stroke was 58.9% and specificity 99.8%; for ischaemic stroke, 38.7% and 99.9%, respectively. Misclassification was highest for endocrine-metabolic and genito-urinary codes.
Conclusions:
- National mortality coding underestimated the true proportion of CHD deaths by 13.6% and stroke deaths by 50.8% in the cohort.
- Inaccurate cause-of-death classification can significantly impact findings in epidemiological studies.
- Improved accuracy in mortality coding is necessary for reliable CVD burden estimation and research.
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.
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