Is the Charlson Comorbidity Index useful for predicting trauma outcomes?

Background: Inclusion of a measure of comorbidity in trauma scoring has been suggested due to the potential for preexisting conditions to impact on patient outcomes, but studies have reported varied results. The Charlson Comorbidity Index (CCI) includes 19 diseases weighted on the basis of their association with mortality, and can be extrapolated from International Classification of Diseases, Ninth Revision (ICD-9) codes for administrative databases. Objectives: To evaluate the CCI as a predictor of trauma outcome. Methods: Major trauma patient data from the Victorian State Trauma Registry (VSTR) were used to evaluate the CCI (n = 2,819). The CCI was scored from ICD-10 codes through modification of a previous method of mapping ICD-9 codes to the CCI. Logistic regression was used to determine the association between the CCI and mortality, the effect of adding the CCI to the Trauma and Injury Severity Score (TRISS) methodology, and the impact of adding the CCI to a modification of the TRISS methodology. Model performance was assessed through discrimination and calibration. Results: The CCI was associated with death (p < 0.001), but adding the CCI to TRISS [area under the receiver-operating characteristic curve (AUC) 0.86; 95% CI = 0.84 to 0.88] did not result in improved discrimination over TRISS alone (AUC 0.83; 95% CI = 0.81 to 0.86). Modifying TRISS methodology, with age left as a continuous variable, performed better than the original TRISS (AUC 0.91; 95% CI = 0.89 to 0.92), but the addition of the CCI did not further improve this model (AUC 0.91; 95% CI = 0.89 to 0.92). Conclusions: While the CCI can be extrapolated from ICD codes and provides a measure of comorbid condition severity and was associated with mortality, addition of the CCI to prediction models did not result in a substantial improvement in performance.