Published: 14-01-2021 12:56 | Updated: 14-01-2021 12:57

Adaptation of the Charlson comorbidity index (CCI) for register-based research in Sweden

Tiles that reads register.
Tiles that reads register. Photo: Nick Youngson

The Charlson co-morbidity index (CCI) is a disease index that was originally created to predict short-term mortality but is increasingly used as a proxy for comorbidity burden, and is often used as a co-variate, for instance in regression models. There are currently several available versions of the CCI. The existence of multiple morbidity indices creates confusion, increases the risk of mistakes and requires individual researchers to spend considerable time examining included codes.

In an effort involving 6 Swedish universities, 16 researchers explored diagnostic codes and adapted the CCI to a Swedish setting.

– We sought to create a cohesive system in which the contents of different international classification of disease codes (ICD, versions 7, 8, 9 and 10) were harmonized, says Professor Jonas F Ludvigsson, pediatrician at Örebro University Hospital and professor at the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet.

– We felt that there was a need to better distinguish between mild, moderate or severe disease in the CCI. But more importantly we also wanted to create scripts for common statistics software to facilitate the work of researchers, adds Ludvigsson.

The researchers reviewed all codes of the CCI, and in the paper they included both Swedish and English descriptions. These descriptions are included in a 15-page-table in the paper.

– I want to stress that this was a truly collaborative paper where experts from a large number of fields contributed. This was needed to attain a high quality of the coding. I also want to mention three KI statisticians and database managers; Bjorn Roelstraete, Jonas Söderling and Mariam Lashkariani who helped out with the creation of the scripts in R, SAS and STATA.” says Ludvigsson.

Additional information

R, SAS and STATA scripts can be found at:

The CCI is a list of international classification of disease (ICD) codes for the following diseases: myocardial infarction, congestive heart failure, peripheral vascular disease, cerebrovascular disease, pulmonary diseases, rheumatic disease, dementia, hemiplegia, diabetes, chronic kidney disease, liver disease, peptic ulcer disease, cancer and HIV/AIDS.

Dr Ludvigsson coordinates a study on behalf of the Swedish IBD quality register (SWIBREG). That study has received funding from the Janssen corporation.


Jonas F. Ludvigsson, Peter Appelros, Johan Askling, Liisa Byberg, Juan-Jesus Carrero, Anna Mia Ekström, Magnus Ekström, Karin Ekström Smedby, Hannes Hagström, Stefan James, Bengt Järvholm, Karl Michaelsson, Nancy L. Pedersen, Helene Sundelin, Kristina Sundquist, Johan Sundström. Adaptation of the Charlson comorbidity index for register-based research in Sweden. Clinical Epidemiology, 2021:13.

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