Methods Inf Med 2017; 56(05): 401-406
DOI: 10.3414/ME17-01-0051
Schattauer GmbH

The Charlson Comorbidity Index in Registry-based Research

Which Version to Use?
Nele Brusselaers
1  Centre for Translational Microbiome Research (CTMR), Department of Microbiology, Tumor- and Cell Biology, Karolinska Institutet, Stockholm, Sweden
2  Science for Life Laboratory (SciLifeLab), Stockholm, Sweden
Jesper Lagergren
3  Upper Gastrointestinal Surgery, Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
4  Division of Cancer Studies, King’s College London, UK
› Author Affiliations
Further Information

Publication History

received: 17 May 2017

accepted in revised form: 28 August 2017

Publication Date:
24 January 2018 (online)


Background: Comorbidities may have an important impact on survival, and comorbidity scores are often implemented in studies assessing prognosis. The Charlson Comorbidity index is most widely used, yet several adaptations have been published, all using slightly different conversions of the International Classification of Diseases (ICD) coding.

Objective: To evaluate which coding should be used to assess and quantify comorbidity for the Charlson Comorbidity Index for registry-based research, in particular if older ICD versions will be used.

Methods: A systematic literature search was used to identify adaptations and modifications of the ICD-coding of the Charlson Comorbidity Index for general purpose in adults, published in English. Back-translation to ICD version 8 and version 9 was conducted by means of the ICD-code converter of Statistics Sweden.

Results: In total, 16 studies were identified reporting ICD-adaptations of the Charlson Comorbidity Index. The Royal College of Surgeons in the United Kingdom combined 5 versions into an adapted and updated version which appeared appropriate for research purposes. Their ICD-10 codes were back-translated into ICD-9 and ICD-8 according to their proposed adaptations, and verified with previous versions of the Charlson Comorbidity Index.

Conclusion: Many versions of the Charlson Comorbidity Index are used in parallel, so clear reporting of the version, exact ICD- coding and weighting is necessary to obtain transparency and reproducibility in research. Yet, the version of the Royal College of Surgeons is up-to-date and easy-to-use, and therefore an acceptable co-morbidity score to be used in registry-based research especially for surgical patients.