Concept: Charlson Comorbidity Index

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Concept Description

Last Updated: 2009-10-22

    The Charlson Comorbidity Index contains 19 categories of comorbidity, which are primarily defined using ICD-9-CM diagnoses codes (a few procedure codes are also employed). Each category has an associated weight, taken from the original Charlson paper 1 , which is based on the adjusted risk of one-year mortality. The overall comorbidity score reflects the cumulative increased likelihood of one-year mortality; the higher the score, the more severe the burden of comorbidity.

    Use the Charlson Comorbidity Index with caution - the ICD-9-CM codes used in the program can refer either to complication or comorbidity diagnoses. Unless these can be reliably differentiated it is possible that the burden of comorbid disease might be overestimated. The best way to avoid the confusion of complications with comorbidities is to remove the complications. For hospital datasets this can be done using the diagnosis type variable.

    When this is not possible the use of this macro is not precluded: the effect of complications on the comorbidity estimates provided by this macro is limited since individual diagnoses are not used directly in calculating the comorbidity score. Rather, these determine attribution to comorbidity categories which are scored as binary variables. This binary attribution within a comorbidity category limits the effect of complications since both the comorbidity and complication codes often fall in the same disease category.

    Recent work by Quan et al. (2005) has modified the Charlson Comorbidity Index (ICD-9-CM codes) and updated the coding to ICD-10. These updates are presented towards the end of this concept.
How the Index Works
    The Index may be calculated either for a single record (separation) or over a defined period of time prior to an index event. Every diagnosis and procedure code is analyzed to see if it falls within one of the 16 comorbid conditions. If one of these is found, a flag (1) for that condition is set. These flags are weighted appropriately and summed to generate values:
    PCHRLSON - Charlson variable computed from admissions prior to and including the event.

    XCHRLSON - Charlson variable computed from the event admission only.

    PCOMP - Component variables for the Charlson variable observed on admissions prior to the event. (Note: there are 61 component variables)

    XCOMP - Component variables for the Charlson variable which were observed on the event admission. (Note: There are 61 component variables)

    AGGREGATES - Combinations of PCOMP and XCOMP variables which are used for final determination of the Charlson score.
ICD-9-CM to ICD-10 Conversion
    Several studies have translated the Charlson Comorbidity Index from the usage of ICD-9-CM codes to ICD-10 codes for the study of complications and comorbidities. Quan et al. "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." Halfon et al. carried out the translation to ICD-10 from the Deyo adaptation of the Charlson comorbidity index. The following link is a table comparing Halfon's and Quan's translations of the Charlson Comorbidity Index using ICD-10 codes. Excel ] Note: The table also includes Quan's translation of the Elixhauser index.

    SAS CODE: developed from Quan et al. (2005).
    Note: This code has not been validated by MCHP.

    The Charlson Comorbidity Index should only be used with the Hospital Discharge Abstract data and NOT with the medical services/physician claims data. The reason for this is because the Index, in some instances, requires the degree of specificity only found in the 4- and 5-digit ICD-9 codes provided in the Hospital Discharge Abstracts data. Medical services/physician claims data only contains 3-digit ICD-9-CM codes.

SAS code and formats 

Related concepts 

Related terms 



  • 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)
  • 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)


  • comorbidity
  • complications
  • Disease
  • Health Measures
  • mortality

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