Clarification on the categorization of comorbidities

Abstract

Comorbidities are coexisting diseases that are distinct from the primary illness for which a patient seeks health care services 1. Comorbidity may affect detection, prognosis, therapy, and outcome of the primary disease. We recently published a paper evaluating the role of comorbidities in the survival of patients with myelodysplastic syndromes, in which Charlson index was utilized as the measure of comorbidities 2. Charlson et al. developed a weighted index measure of comorbidities based on medical records review and identified a total of 19 conditions that influence mortality 3. Both the number and the seriousness of comorbid conditions were taken into account. Each of the 19 conditions was assigned a weight (0 - 6) according to its potential for influencing mortality. A patient's comorbidity index would be the sum of all weighted comorbidities. A higher score on the Charlson index indicates a greater burden of comorbid conditions. Later, Deyo et al. adapted the Charlson index for use with the ICD-9-CM diagnostic and procedure codes available in administrative datasets 4. Researchers at the National Cancer Institute subsequently developed a SAS macro to calculate Charlson index for linked SEER*Medicare data (http://healthservices.cancer.gov/seermedicare/program/comorbidity.html). We adopted this method to calculate Charlson index for the more than 2,000 patients included in our study.