Understanding the High Prevalence of Low-Prevalence Chronic Disease Combinations: Databases and Methods for Research. Health Level Seven International Grouper System


Major Diagnostic Categories (MDC)
Sponsorship: Health Level Seven International
Description: MDCs are used to group diagnoses into 25 broad categories according to a single organ system or etiology. To some degree, these categories have also been shown to be associated with some medical specialties ( e.g., ENT).
Purpose/Use: MDCs have been used to group diagnoses into categories for a variety of different types of research. However, this system was originally created to test whether DRGs were clinically coherent. Since then, MDCs have been used to look at healthcare utilization and costs related to diagnoses from a broad perspective.
Coding Family: International Classification of Diseases, Ninth Revision (ICD- 9). DRG and CCS condition categories can also be mapped to MDCs.
Grouping Methodology: MDCs are formed by dividing all possible principal diagnosis codes into 25 mutually exclusive diagnosis categories, which correspond to a single organ system or etiology. Separate mapping systems are available to group ICD-9 codes, DRGs and CCS group into major diagnostic categories. MDC1 through MDC23 are grouped strictly according to principal diagnosis. Patients with at least two significant trauma diagnosis codes are grouped under MDC 24. Patients with a principal diagnosis of HIV infection of principal diagnosis of a significant HIV-related condition and a secondary diagnosis of HIV are grouped into MDC 25.1
Level of Diagnosis Aggregation: Diagnosis codes are grouped in 25 categories.
Number of Codes Included: Not specified
Number of Codes Excluded: Not specified
Methodological Considerations:

This grouping system provides researchers with a quick and efficient mechanism to group diagnosis codes for the purpose of drawing general conclusions about different major diagnostic groups.

This grouping system lacks granularity to study specific diagnoses that have aggregated up into larger major diagnostic categories.

Related Data Sources: Claims data, DRG & CCS groups (mapping)
Used in Disease Complexity Research: Yes2


1 Utah Department of Health. Major Diagnostic Categories. 2013. http://health.utah.gov/opha/IBIShelp/codes/MDC.htm

2 Kuwabara K et al. The association of the number of comorbidities and complications with length of stay, hospital mortality and LOS high outlier, based on administrative data. Environ Health Prev Med.2008;13(3):130–7.


View full report


"rpt_LowPrevMCCData.pdf" (pdf, 1.37Mb)

Note: Documents in PDF format require the Adobe Acrobat Reader®. If you experience problems with PDF documents, please download the latest version of the Reader®