Understanding the High Prevalence of Low-Prevalence Chronic Disease Combinations: Databases and Methods for Research. Agency for Healthcare Research and Quality Grouper System


Clinical Classifications System (CCS)
Sponsorship: Agency for Healthcare Research & Quality

AHRQ’s Clinical Classifications Software (CCS) is a system that clusters patient diagnoses and procedures into a number of clinically meaningful categories for analytic purposes. The CCS consists of two related classifications systems:

1) Single-level CCS, which is used to rank diagnoses and procedures and for risk adjustment,

2) Multi-level CCS, which is used to evaluate large groups of condition and procedures.1

Purpose/Use: The CCS system was created to allow health plans, policy makers, and researchers to understand patterns of diagnoses and procedures in terms of cost, utilization and outcomes.
Coding Family: International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM)
Grouping Methodology:

The single-level CCS system aggregates over 14,000 ICD-9- CM codes into 285 mutually exclusive categories. The majority of these categories are clinically homogenous. However, some heterogeneous categories are needed to combine several less common individual conditions within a body system.1

The multi-level CCS system aggregates single-level CCS groupings and ICD-9 codes into a hierarchical structure to create broader clinical categories (i.e. infectious disease, hypertension, etc.).This hierarchical structure has 18 categories, each with 4 levels of granularity.1

Level of Diagnosis Aggregation: ICD-9-CM codes are aggregated into 285 mutually exclusive categories.
Number of Codes Included: 14572
Number of Codes Excluded: None
Methodological Considerations: The CCS creates diagnosis groupings that are clinically homogenous. As it includes all ICD-9-CM codes, it is a more comprehensive grouping system compared to other grouping methodologies.
Related Data Sources: Healthcare Cost and Utilization Project Data & claims data
Used in Disease Complexity Research: Yes2


1 Elixhauser A, Steiner C, Palmer L. Clinical Classifications Software (CCS), 2013. U.S. Agency for Healthcare Research and Quality. Available: http://www.hcup-us.ahrq.gov/.

2 Yu W, Ravelo A, Wagner TH, et al. Prevalence and costs of chronic conditions in the VA health care system. Med Care Res Rev. 2003; 60(3 Suppl):1462-167S.


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