Developing Country-Specific Charlson Comorbidity Index Mappings for Use with German Administrative Data: Methodological Comparative Study.

Authors

Piotr Paweł Sokołowski, Michael Hagmann, Máté E Maros, Gaetan Kamdje Wabo, Josefine Maria Meerjanssen, Fabian Siegel

Published in

JMIR medical informatics. Jul 12, 2026. Epub Jul 12, 2026.

Abstract

The Charlson Comorbidity Index (CCI) is widely used to quantify comorbidity burden in observational research. Applying it to real-world data requires accurate ICD-based mappings. The commonly used mapping by Quan et al. (2005) does not reflect current German coding standards.
To develop year-specific mappings (2004 to 2026) based on the German Modification of ICD-10 for the CCI with an open-source implementation and compare them with the mapping by Quan et al.
For each year, mappings were curated via independent dual review with consensus. In 515,827 inpatient cases from a German tertiary center (2010-2024), year-appropriate mappings and Quan's mapping were applied and the results pooled into two respective datasets that were subsequently compared. Agreement was assessed using the Intraclass Correlation Coefficient (ICC) (two-way mixed-effects model for absolute agreement based on single measurement), and the significance of the discordances was measured using McNemar's test.
Agreement was very high; 3.13% of cases differed. A single code was present in 49% of the discordant cases and was intentionally excluded in the new mappings as not diagnostic for the category it was assigned to. Discordant results were found in 9 out of 17 categories with the leading categories "peripheral vascular disease", "mild liver disease" and "severe liver disease" being present in respectively 52%, 17% and 16% of the discordant cases. After filtering the dataset to only include observations with any diagnosis of a malignant disease, 6.86% of cases differed, and 79% of those differences were caused by the category "peripheral vascular disease", suggesting significant discrepancies for specific research questions.
We provide transparent, year-specific ICD-10-GM (2004-2026) mappings and an open-source tool for CCI calculation. The mappings align with current German coding practice and enable reproducible, year-appropriate comorbidity adjustment using administrative data.

PMID:
42593349
Bibliographic data and abstract were imported from PubMed on 13 Aug 2026.

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