Short summary

Charlson Comorbidity Index (CCI) is in much use in current health research to capture the comorbidity burden of patients. As CCI was developed in the 1980's in patient populations in the USA, its current validity in unclear. We aim to systematically review validation studies of CCI to inform the application and interpretation of CCI in current health research.

Rationale

In most health research not only the investigated exposures, but also patients' comorbidities influence health outcomes and survival. To catch this effect Charlson and colleagues in 1987 developed the Charlson Comorbidity Index (CCI) to classify comorbidities according to strength of association with mortality and developed a score including 19 specific comorbidities each associated with a score between 1 and 6 dependent on how strong they were associated with mortality. Since then CCI has become the most used measure for comorbidity, both as an explanatory variable and to adjust or stratify for comorbidities to avoid confounding in many areas of health research.

While CCI in its different versions has been validated on a large variety of cohorts almost all of these only contain hospitalized patients, or in some cases outpatients, but not a representative sample of the general population, while at the same time CCI today routinely is used as a measure of comorbidity for population samples, for instance in studies investigating incidence of diseases, effectiveness of screening programs study of chronic diseases or public health developments. Moreover, the latest of the often referenced validation cohorts ended in 2008, and due to the large improvements in treatment and management of diseases in recent years, it is unclear how the validity of CCI performs in current populations. The most recent systematic review by Yurkovich and colleagues focused on comorbidity indexes applied on administrative data but focused mainly on comparison between different comorbidity indexes and less on the validity of CCI in different populations. Moreover, this review included papers only up till September 2012, hence a current overview of the validity of CCI is lacking. 

We aim to carry out a systematic review investigating the status of validations of both versions of CCI from 1987 to today in the literature to detect degree of evidence for validity of CCI and to inform a possible future validation study. 

Description of the cohort

Systematic review

Collaborating researchers and departments

OPEN, Odense University Hospital and Department of Clinical Research, University of Southern Denmark

• Associate professor Sören Möller, PhD
• Dalia Fikrisellasie, MHS
• Project coordinator Lene Bjerregaard, PhD
• Associate professor Mette Bliddal, PhD

Publications associated with the project

Möller, S., Bliddal, M. & Rubin, K.H. Methodical considerations on adjusting for Charlson Comorbidity Index in epidemiological studies. Eur J Epidemiol 36, 1123-1128 (2021). https://doi.org/10.1007/s10654-021-00802-z