Concept: Charlson Comorbidity Index

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Concept Description

Last Updated: 2014-10-06

Introduction
    This concept contains information on the Charlson Comorbidity Index including: a basic description of the Charlson Comorbidity Index and the development and changes to this index over time as presented in different research. The concept also includes access to different versions of SAS® code for running the Charlson Comorbidity Index.
Description of the Charlson Comorbidity Index
    The Charlson Comorbidity Index is a method of categorizing comorbidities based on the International Classification of Diseases (ICD) diagnoses and procedure codes of individual patients using administrative data, such as Hospital Discharge Abstracts data. Each comorbidity category has an associated weight, based on the adjusted risk of one-year mortality, and the sum of all the weights results in a single comorbidity score for a patient. A score of zero indicates that no comorbidities were found. The higher the score, the more likely the predicted outcome will result in higher resource use or mortality.

    Over time, there have been variations in the Index used in different research. A summary of these variations include:

    • the original Index was developed with 19 categories, but has been adjusted to 17 categories;
    • the list of specific ICD codes that are used to identify different categories of comorbidity have been adjusted; and
    • the original weights developed for use with the Index have also been adjusted.

    For more information on these changes, please read the Research Using the Charlson Comorbidity Index section below.

    For a list of 17 categories used in the Charlson Comorbidity Index, please see Table 1. ICD-9-CM and ICD-10 Coding Algorithms for Charlson Comorbidities from (Quan et al., 2005).
Research Using the Charlson Comorbidity Index
    The Charlson Comorbidity Index was originally developed in 1987. The following chronological sections highlight some of the significant developments and changes that have occurred over time in research related to the Charlson Comorbidity Index:

    1. Charlson et al. (1987)
    In the original publication "A new method of classifying prognostic comorbidity in longitudinal studies: development and validation" by Charlson et al. (1987), they identified 19 categories of comorbidity and weights were developed for each category based on the adjusted relative risk of one-year mortality. All of the individual weights are summed to produce a single comorbidity score for each patient.

    2. Deyo et al. (1992)

    In the publication "Adapting a clinical comorbidity index for use with ICD-9-CM administrative databases" by Deyo et al. (1992), they assigned corresponding ICD-9-CM codes for each category of the Charlson Comorbidity Index. Two of the original categories, "Leukemia" and "Lymphomas", were combined in the "Any Malignancy" category, thus resulting in a total of 17 different categories.

    3. Romano et al. (1993)

    In the publication "Further evidence concerning the use of a clinical comorbidity index with ICD-9-CM administrative data" by Romano et al. (1993), they compared the list of ICD codes developed by Deyo with a different set of codes, referred to as the Dartmouth-Manitoba codes, developed for use with the Charlson Comorbidity Index. The study illustrated that the assignment of ICD-9-CM codes to the Charlson Comorbidity Index is not straightforward and depends on the type of data and its availability, and concluded that in some cases the differences will have little or a significant impact on the measure of comorbidity.

    4. Roos et al. (1997)

    In the publication "Complications, comorbidities, and mortality: improving classification and prediction" by Roos et al. (1997), they investigated the possible confounding nature of complications (conditions arising after the beginning of hospital treatment) and found the existence of a variable called "Diagnosis Type" in the data could be used to separate complications from comorbidities.

    NOTE: Information relevant to this early work by MCHP on the Charlson Comorbidity Index is available from Charlson Comorbidity Index - Archived Concept Information or from the LINKS section below -- see MCHP - Archived Charlson Concept Information.

    5. Halfon et al. (2002)

    In the publication "Measuring potentially avoidable hospital readmissions" by Halfon et al. (2003), they translated the ICD-9-CM diagnoses codes from the Deyo adaptation of the Charlson Comorbidity Index into ICD-10-codes. Appendix C in the article presents the ICD-10 codes and assigned weights that were developed by Halfon.

    6. Schneeweiss et al. (2003)

    In the publication "Improved comorbidity adjustment for predicting mortality in Medicare populations" by Schneeweiss et al. (2003), they investigated methods for adjusting comorbidity measures in order to improve the prediction of mortality in Medicare populations. This research used Romano's adapted Charlson Comorbidity Index and came up with adjusted weights for using the index - see Table 4: Conditions According to the Romano Adaptation of the Charlson Comorbidity Index for Use with Claims Data with original Charlson Index Weights and Weights Derived from New Jersey Medicare Data in the the full text publication available from the PubMed Central web site at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1360935/pdf/hesr_165.pdf - accessed October 3, 2014.
    7. Quan et al. (2005)
    In the publication "Coding algorithms for defining comorbidities in ICD-9-CM and ICD-10 administrative data" by Quan et al. (2005), they "conducted a multistep process to develop ICD-10 coding algorithms to define Charlson and Elixhauser comorbidities in administrative data and assess the performance of the resulting algorithms." They also followed Deyo's coding algorithm, which led to modifications and enhanced coding algorithms for the index.

    The Charlson Comorbidity Index SAS® code developed for this project is available - see the SAS Code section below.

    Comparison of Halfon and Quan's ICD-10 Coding
    The following link is a table comparing Halfon's and Quan's translations of the Charlson Comorbidity Index using ICD-10 codes: Halfon-Quan Comparison of Charlson ICD-10 Codes. Note: The table also includes Quan's translation of the Elixhauser index.
    8. Sundararajan et al. (2007)
    In the publication "Cross-national comparative performance of three versions of the ICD-10 Charlson Index" by Sundararajan et al. (2007), they compared the performance of three different versions of the Charlson Comorbidity Index using ICD-10 coding and found that all three version performed satisfactorily.
    9. Li et al. (2008)
    In the publication "Risk adjustment performance of Charlson and Elixhauser comorbidities in ICD-9 and ICD-10 administrative databases" by Li et al. (2008), they assessed the performance of the Charlson Comorbidity Index and the Elixhauser Comorbidity Index using ICD-10 coding systems and found that the "change in coding algorithms did not influence the performance of either ... [index] ... in the prediction of outcome".
    10. Garland et al. (2012)
    In the MCHP Deliverable "The Epidemiology and Outcomes of Critical Illness in Manitoba" by Garland et al. (2012), they used the Charlson Comorbidity Index, as adapted by Deyo and Quan, as one of three systems for assessing chronic comorbid health conditions. For more information on the use of the Charlson Comorbidity Index and the results from this research, please read the following sections:

    11. Lix et al. (IN PROGRESS - 2014)
    In the MCHP Deliverable "CancerCare Manitoba Data Acquisition into the Repository" by Lix et al. (IN PROGRESS - 2014), the Charlson Comorbidity Index algorithm is being modified by MCHP so that it can be used with 3-digit ICD-9-CM codes that are available in the Medical Services (Physician Claims) data. This will broaden the scope of comorbidity found in the population.

    The use of 3-digit codes requires a modification to the original list of ICD codes for some of the categories in the Charlson Comorbidity Index. These modifications include:

    • combining the two diabetes conditions, "Diabetes With Complication" and "Diabetes Without Complications", into one category because it is not possible to differentiate between the two using 3-digit codes. Anyone with ICD code "250" is categorized into the less severe "Diabetes Without Complications" category. This modification results in 16 categories in the 3-digit version of the Index.
    • a decision has to be made to include/exclude certain codes in specific categories due to the specificity issue. For a complete list of the 3-digit ICD-9 codes used for each category and the choices that were made for inclusion/exclusion of codes, please see Using 3-Digit ICD-9-CM Codes with the Charlson Comorbidity Index.

      See the Cautions / Limitations section for more information on using 3-digit ICD codes with the Index.

      For the SAS code related to working with 3-digit ICD-9 codes in the Charlson Comorbidity Index, please see MCHP SAS Code - Charlson Index - Working with 3-digit ICD-9-CM Codes in the SAS CODE section below.
SAS Code
Cautions / Limitations
    The following cautions apply to using the Charlson Comorbidity Index:

    1. Before using the Charlson Comorbidity Index, please differentiate between diagnoses that are complications and comorbidity related -- complications should NOT be used in the calculation of the index. Unless these can be reliably differentiated, it is possible that the burden of disease may be overestimated. The best way to avoid the confusion of complications with comorbidities is to identify diagnoses with a Diagnosis Type (DXTYPE) = "C" (where "C" = "Complication") or = "2" (where "2" = "Post-Admit Comorbidity") and not include them.
    2. The Charlson Comorbidity Index is designed to be used with specific ICD coding (5-digit ICD-9-CM codes and 7-digit ICD-10 codes) that is found in the Manitoba Hospital Discharge Abstracts data. This is due to the specificity required to distinguish between diagnoses that should / should not be included in the index and to be able to properly identify and place codes into the corresponding category.
    3. In general, using only 3-digit ICD codes to calculate the Charlson Comorbidity Index is not recommended because it lacks the specificity required to properly categorize diagnoses and conditions.

SAS code and formats 

Related concepts 

Related terms 

Links 

References 

  • Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chronic Dis 1987;40(5):373-383. [Abstract] (View)
  • Deyo RA, Cherkin DC, Ciol MA. Adapting a clinical comorbidity index for use with ICD-9-CM administrative databases. Journal of Clinical Epidemiology 1992;45(6):613-619. [Abstract] (View)
  • Garland A, Fransoo R, Olafson K, Ramsey C, Yogendran M, Chateau D, McGowan K. The Epidemiology and Outcomes of Critical Illness in Manitoba. Winnipeg, MB: Manitoba Centre for Health Policy, 2012. [Full Report] [Summary] (View)
  • Halfon P, Eggli Y, van Melle G, Chevalier J, Wasserfallen JB, Burnand B. Measuring potentially avoidable hospital readmissions. J Clin Epidemiol 2002;55(6):573-587. [Abstract] (View)
  • Li B, Evans D, Faris P, Dean S, Quan H. Risk adjustment performance of Charlson and Elixhauser comorbidities in ICD-9 and ICD-10 administrative databases. BMC Health Services Research 2008;14(8):12. [Abstract] (View)
  • Quan H, Sundararajan V, Halfon P, Fong A, Burnand B, Luthi JC, Saunders LD, Beck CA, Feasby TE, Ghali WA. Coding algorithms for defining comorbidities in ICD-9-CM and ICD-10 administrative data. Med Care 2005;43(11):1130-1139. [Abstract] (View)
  • Quan H, Parsons GA, Ghali WA. Validity of information on comorbidity derived rom ICD-9-CCM administrative data. Med Care 2002;40(8):675-685. [Abstract] (View)
  • Romano PS, Roos LL, Jollis JG. Adapting a clinical comorbidity index for use with ICD-9-CM administrative data: differing perspectives. J Clin Epidemiol 1993;46(10):1075-1079. [Abstract] (View)
  • Romano PS, Roos LL, Jollis JG. Response: Further evidence concerning the use of a clinical comorbidity index with ICD-9-CM administrative data. J Clin Epidemiol 1993;46(10):1085-1090. [Abstract] (View)
  • Roos LL, Stranc L, James RC, Li J. Complications, comorbidities, and mortality: improving classification and prediction. Health Serv Res 1997;32(2):229-238. [Abstract] (View)
  • Schneeweiss S, Wang PS, Avorn J, Glynn RJ. Improved comorbidity adjustment for predicting mortality in Medicare populations. Health Serv Res 2003;38(4):1103-1120. [Abstract] (View)
  • Sundararajan V, Quan H, Halfon P, Fushimi K, Luthi JC, Burnand B, Ghali WA, International Methodology Consortium for Coded Health Information (IMECCHI). Cross-national comparative performance of three versions of the ICD-10 Charlson Index. Medical Care 2007;45(12):1210-1215. [Abstract] (View)

Keywords 

  • Charlson Index
  • comorbidity
  • complications
  • Disease
  • Health Measures
  • mortality


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