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Ischemic heart disease and hypertension: effect of disease coding on epidemiologic assessment
1Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control, Atlanta, GA 30333.
Insights
Changes in disease coding (ICD) created discontinuities in Ischemic Heart Disease (IHD) and Hypertension (HBP) data. These coding changes impacted trends differently across sex-race groups, necessitating careful consideration for future classifications.
Area of Science:
- Epidemiology
- Medical Informatics
- Public Health
Background:
- The transition between the International Classification of Diseases, 8th and 9th revisions (ICD-8 to ICD-9) introduced significant coding alterations for Ischemic Heart Disease (IHD) and Hypertension (HBP).
- These coding changes resulted in notable discontinuities in the recorded data for IHD and HBP.
- The impact of these discontinuities was not uniform across different sex-race demographic groups.
Purpose of the Study:
- To investigate the nature and extent of discontinuities in IHD and HBP coding introduced by the ICD revision.
- To examine how these coding changes differentially affected mortality trends across various sex-race groups.
- To highlight the importance of epidemiologic continuity for accurate trend assessment in population subgroups.
Main Methods:
- Analysis of coding changes in ICD-8 and ICD-9 for Ischemic Heart Disease (IHD) and Hypertension (HBP).
- Examination of discontinuities by component ICD codes across sex-race groups.
- Assessment of changes in the rate of decline for IHD and HBP mortality post-ICD revision.
Main Results:
- Major discontinuities were observed for IHD and HBP following the ICD revision.
- These discontinuities varied in magnitude and direction among different sex-race groups when analyzed by component ICD codes.
- The rate of decline in IHD and HBP mortality also changed post-revision, with generally slower declines observed among Black populations compared to White populations.
Conclusions:
- The ICD revision introduced significant coding discontinuities impacting IHD and HBP data, with differential effects across sex-race groups.
- Observed variations in mortality decline rates between racial groups may be influenced by coding practices.
- Future revisions, such as ICD-10, require careful attention to maintaining epidemiologic continuity to ensure accurate population subgroup trend analysis.
Abstract:
During the changeover from the eighth to the ninth revision of the "International Classification of Diseases: Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death" (ICD), there were several major alterations of coding for the rubrics Ischemic Heart Disease (IHD) and Hypertension (HBP). As expected, these changes caused major discontinuities for IHD and HPB. These discontinuities were not, however, uniform over sex-race groups. When examined by component ICD codes, the discontinuities were found to vary in both magnitude and direction among the groups. In addition to discontinuity, there was a change in the rate of decline for IHD and HBP after the changeover. This rate of decline varied as well by sex-race group. In general, the decline among blacks was slower than among whites. Earlier studies that assessed IHD mortality have used different groupings of ICD codes to obviate the discontinuity, and researchers have observed a similar differential decline. These results should be viewed with caution because of the potential impact of differential coding on sex-race groups. As preparations are made for ICD-10, special attention should be given to the preservation of epidemiologic continuity to provide better assessment of trends in population subgroups.