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The Enhanced Charlson comorbidity index provides a reproducible tool to identify patients with multiple chronic diseases in a universally applicable, transparent, and auditable method.

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Published in 1987, the Charlson Comorbidity Index was originally developed to measure the aggregate prognostic burden  of comorbidity disease to  predict mortality. It was designed to enable researchers to control for the prognostic impact of other chronic diseases on the outcomes of patients with a specific chronic disease

  • Without such a tool, investigators often excluded patients with other chronic diseases from their studies to eliminate the potential of ‘confounding’. For example, studies of patients with diabetes might exclude patients with cancer or congestive heart failure to make certain that they did not confound the outcomes.
  • Such exclusions limited the number of patients to whom the study results applied.

Cited in more than 14,519 publications, the Charlson comorbidity index is the most extensively validated measure of the prognostic impact of multiple chronic illnesses.
The original comorbidity index was a weighted measure of the burden of chronic disease that predicts long term prognosis and outcomes.  The original index assigns a numerical value or “weight” from 1,2,3 or 6 to  19 specific chronic illnesses. The final score is simply the sum of weighted values.
Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classification of prognostic comorbidity for longitudinal studies: development and validation. J Chron Disease. 1987; 40(5): 373-383.  (link to pdf)

The comorbidity index was adapted to predict costs of primary care patients with chronic disease.  This includes the 3 additional conditions and one medication. link to pdf

Charlson ME, Charlson RE, Marinopoulos SS, Briggs WM, Hollenberg JP. The Charlson Comorbidity Index is adapted to predict costs of chronic disease in primary care patients. J Clin Epidemiol. 2008; 61:1234-40.

Subsequently, the comorbidity index was employed why disease management programs cannot reduce costs.

Charlson M, Charlson RE, Briggs W, Hollenberg J.  Can disease management target patients most likely to generate high costs?  The impact of comorbidity.  Journal of General Internal Medicine. 2007; 22: 464-469. Link to pdf
Recent work has shown that the comorbidity index predicts future costs.
Charlson ME, Wells MT, Kanna B, Dunn V, Michelen W. Medicaid Managed Care: How to target efforts to reduce costs. BMC Health Services Research In press
Charlson ME, Wells MT, Ullman R, King F, Shmukler C. The Charlson comorbidity index can be used prospectively to identify patients who will incur high future costs. PLOS One. In Press