MISCLASSIFICATION OF CORONARY HEART-DISEASE IN MORTALITY STATISTICS -EVIDENCE FROM THE WHO-MONICA GHENT-CHARLEROI STUDY IN BELGIUM

Study objective-To validate the Belgian vital statistics for coronary heart disease (CHD) on the basis of an independent acute myocardial in farction (AMI) register, carried out as part of the WHO-MONICA project . Design-Records of fatal cases of AMI in the WHO-MONICA register were individually linked to the corresponding death certificates. Setting- Since 1983, the WHO-MONICA Collaborating Centre Ghent/Charleroi regist ers all fatal and non-fatal AMI in the age group 25-69 years in two ge ographical areas, Ghent in the northern Dutch speaking part and Charle roi in the southern French speaking part of Belgium. Registration is d one according to the MONICA protocol. The official vital statistics in Belgium are published on a yearly basis. They are essentially a refle ction of the ''underlying'' causes of death, coded according to the 9t h revision of the International Classification of Diseases (ICD). The study was undertaken in the period 1983-1991. Main results-Out of a to tal of 741 (Ghent) and 934 (Charleroi) well documented MONICA fatal ca ses of AMI, 492 (66.4%) and 641 (68.6%), respectively, were officially labelled as CHD (ICD code 410-414); 438 (59.1%) and 385 (41.2%), resp ectively, were officially labelled as AMI (ICD code 410). A substantia l fraction of the MONICA AMI cases-27.1% in Ghent and 38.2% in Charler oi-was coded as ''other forms of CHD'' (ICD 411-414) or as ''other for ms of heart disease'' (ICD 420-429). The remaining MONICA AMI cases-13 .8% in Ghent and 20.6% in Charleroi-were classified in either very asp ecific (for example, atherosclerosis, ICD 440) or totally unrelated IC D codes (for example, neoplasm, ICD 140-239). Conclusions-It is conclu ded from the results in this paper that a substantial part of all deat hs caused by CHD in Belgium are labelled with incorrect ICD codes and are therefore misclassified in the official mortality statistics for B elgium. This is partly caused by a ''drainage'' of cases towards less specific CHD related ICD categories. A considerable fraction, however, seems to be absolutely misclassified.