Comorbidity and the association with 1-year mortality in hip fracture patients: can the ASA score and the Charlson Comorbidity Index be used interchangeably?

Abstract

Background: Charlson Comorbidity Index (CCI) has been suggested to be associated with mortality in hip fracture patients, to the same extent as more expensive and time-consuming tools. However, even CCI might be too time-consuming in a clinical setting. Aim: To investigate whether the American Society of Anaesthesiologists score (ASA score), a simple grading from the anaesthesiologist’s examination, is comparable with CCI in the association with 1-year mortality after a hip fracture. Methods: The study population was patients 60 + years registered in the Swedish Hip Fracture Registry with a first-time hip fracture between 1997 and 2017 (N = 165,596). The outcome was 1-year mortality, and the exposures were ASA score and CCI. The association between comorbidity and mortality was described with Kaplan–Meier curves and analyzed with Cox proportional hazards models. Results: The Kaplan–Meier curves showed a stepwise increase in mortality for increasing values of both ASA and CCI. The Hazard Ratios (HRs) for the highest ASA (4–5) were 3.8 (95% Confidence Interval 3.5–4.2) for women and 3.2 (2.8–3.6) for men in the fully adjusted models. Adjusted HRs for the highest CCI (4 +) were 3.6 (3.3–3.9) for women and 2.5 (2.3–2.7) for men. Reference was the lowest score value for both tools. The correlation between the tools was moderate. Conclusions: Both ASA and CCI show a similar stepwise association with 1-year mortality in hip fracture patients, despite measuring different factors and capturing different individuals at risk. Since the ASA score is already accessible for health care staff, it might be preferable to aid in prioritizing vulnerable hip fracture patients at risk of adverse outcomes.