30-day mortality in patients after hip fracture surgery: A comparison of the Charlson Comorbidity Index score and ASA score used in two prediction models

Abstract

Objective: To compare the Charlson Comorbidity Index (CCI) and American Society of Anesthesiologists (ASA) Physical Status Classification used in two prediction models for 30-day mortality after hip fracture surgery.

Study design and setting: Data from 3651 patients (mean age: 83 years) from a Norwegian University Hospital were retrospectively obtained and randomly divided into two cohorts: a model cohort (n = 1825) to develop two prediction models with CCI and ASA as the main predictors, and a validation cohort (n = 1826) to assess the predictive ability of both models. A receiver operating characteristic (ROC) curve determined the best model to predict mortality.

Results: Area under the ROC curve at 30 days was 0.726 (p = 0.988) for both the CCI- and ASA-model. The chosen cut-off-points on the ROC curve for CCI- and ASA-model corresponded to similar model sensitivities of 0.657 and specificities of 0.680 and 0.679, respectively. Hence, each model predicts correctly 66% (n = 96) of the mortalities and 68% (n = 1132 and n = 1131) of the survivals. 23% (n = 33) of the mortalities were predicted by neither model.

Conclusion: The CCI- and ASA-model had equal predictive ability of 30-day mortality after hip fracture. Considering the effort involved in calculating Charlson Comorbidity Index score, the ASA score may be the preferred tool to predict the 30-day mortality after hip fracture.

Keywords: ASA; Charlson comorbidity index; Comorbidity; Hip fracture; Mortality.