TRANSPARENCY OF CHARLSON COMORBIDITY INDEX (CCI) CODE DEFINITIONS IN REAL-WORLD RESEARCH: A SYSTEMATIC REVIEW
Author(s)
Aaron Kamauu, MPH, MS, MD1, Jared H. Kamauu, BA2, Garik Galustjan, MSc3, Michael Buck, PhD4, Craig G Parker, MD, MS5, Kevin Kallmes, BS, MA, JD3;
1Navidence, Inc., Bountiful, UT, USA, 2Navidence Inc, Lehi, UT, USA, 3Nested Knowledge, St. Paul, MN, USA, 4Navidence Inc., Salt Lake City, UT, USA, 5Navidence Inc., Sandy, UT, USA
1Navidence, Inc., Bountiful, UT, USA, 2Navidence Inc, Lehi, UT, USA, 3Nested Knowledge, St. Paul, MN, USA, 4Navidence Inc., Salt Lake City, UT, USA, 5Navidence Inc., Sandy, UT, USA
OBJECTIVES: The Charlson Comorbidity Index (CCI) is widely used in real-world research (RWR) to quantify morbidity burden and predict health outcomes/mortality. Since its introduction in 1987, CCI has had multiple adaptations, including to different coding systems: ICD-9-CM, ICD-10-WHO, ICD-10-CM, and SNOMED CT.[Deyo 1992, Quan 2005, Beyrer 2021, Fortin 2023] Variability across these adaptations is known, with modifications ranging from strict to broad definitions.[Charlson 2022] We assessed the transparency of CCI operational definitions and code lists in published real-world research, specifically examining whether specific CCI code lists were explicitly indicated.
METHODS: We conducted a systematic literature review of RWR studies that utilized CCI. Given the substantial volume of results, we focused on US-based studies published between 2020-2025 investigating type 2 diabetes mellitus (T2DM) or obesity indications. Each publication was evaluated for: explicit publication of CCI code lists, CCI version used (original CCI, age-adjusted, Deyo-CCI, etc.), citations supporting CCI methodology, and contextual application of CCI.
RESULTS: From 42 publications meeting inclusion criteria, only 1 (2.4%) published specific CCI code lists, which matched the Quan 2005 Enhanced ICD-9-CM adaptation. Twenty-five publications (59.5%) provided code lists for other study elements (e.g., inclusion criteria or outcome measures) but not CCI, and sixteen (38.1%) provided no code lists. Citations varied widely when provided (Quan 2005, Quan 2011, Charlson 1987, Deyo 1992, among others), and some researchers modified CCI definitions based on study-specific needs.
CONCLUSIONS: Despite documented variability in CCI code definitions, most RWR studies do not publish specific codes used for CCI, likely assuming CCI represents a universal standard. This lack of transparency impacts accurate interpretation and comparison of results across studies. We strongly recommend researchers publish complete operational definitions and code lists for all study elements, including standardized measures like CCI, to ensure reproducibility and proper contextualization of findings.
METHODS: We conducted a systematic literature review of RWR studies that utilized CCI. Given the substantial volume of results, we focused on US-based studies published between 2020-2025 investigating type 2 diabetes mellitus (T2DM) or obesity indications. Each publication was evaluated for: explicit publication of CCI code lists, CCI version used (original CCI, age-adjusted, Deyo-CCI, etc.), citations supporting CCI methodology, and contextual application of CCI.
RESULTS: From 42 publications meeting inclusion criteria, only 1 (2.4%) published specific CCI code lists, which matched the Quan 2005 Enhanced ICD-9-CM adaptation. Twenty-five publications (59.5%) provided code lists for other study elements (e.g., inclusion criteria or outcome measures) but not CCI, and sixteen (38.1%) provided no code lists. Citations varied widely when provided (Quan 2005, Quan 2011, Charlson 1987, Deyo 1992, among others), and some researchers modified CCI definitions based on study-specific needs.
CONCLUSIONS: Despite documented variability in CCI code definitions, most RWR studies do not publish specific codes used for CCI, likely assuming CCI represents a universal standard. This lack of transparency impacts accurate interpretation and comparison of results across studies. We strongly recommend researchers publish complete operational definitions and code lists for all study elements, including standardized measures like CCI, to ensure reproducibility and proper contextualization of findings.
Conference/Value in Health Info
2026-05, ISPOR 2026, Philadelphia, PA, USA
Value in Health, Volume 29, Issue S6
Code
CO165
Topic
Clinical Outcomes
Disease
SDC: Diabetes/Endocrine/Metabolic Disorders (including obesity)