Comparability between ICD-9 and ICD-10 for the leading causes of death in Spain

BACKGROUND: Implementation of a new Revision of the International Classification of Diseases can create discontinuity in mortality statistics. Revisions are nevertheless essential to ensure international comparability of health statistics. The purpose of this work was to describe the effects of the 10th Revision on mortality statistics by sex and age for leading causes of death in Spain. METHODS: A cross-sectional study of leading causes of death was carried out when the underlying cause of death was coded using both the 9th and 10th Revisions of the International Classification of Diseases in 88,044 death certificates completed in five Autonomous Communities of Spain (Andalusia, Cantabria, Murcia, Navarra, the Basque Country), and the city of Barcelona during the year 1999. Changes introduced by the 10th Revision were described by simple correspondence, percentage of change, Kappa index and comparability ratios between the 10th and the 9th Revision along with their 95% confidence intervals by sex and five-year age group, for the leading causes of death. RESULTS: Under the 10th Revision, AIDS deaths rose by 3.6% (comparability ratio (CR): 1.036; 95% confidence interval (CI):1.015-1.058), arteriosclerosis by 7.1% (CR: 1.071; 95% CI: 1.052-1.090), and drug overdose by 5.2% (CR: 1.052; 95% CI: 0.964-1.140). Mortality due to vascular and senile dementia and non specific dementia declined by 3.2% under the 10th (CR: 0.969; 95% CI: 0.950-0.988). In all the other causes of death the percentage of change regardless of direction was less than 2%. CONCLUSION: The present study found good agreement between ICD-9 and ICD-10 on the leading causes of death and premature mortality in Spain. Causes of death which present differences between Revisions were AIDS, arteriosclerosis, drug overdose and senile dementia. For these causes, the comparability ratios must be taken into account when interpreting mortality statistics.