External validation of the Almelo Hip Fracture Score, a prediction model for early mortality following hip fracture surgery

Purpose Early mortality (< 30 days) in hip fracture patients is as high as 9.6%. Several risk assessment tools have been developed to identify patients at high risk for early mortality. Among them, the Almelo Hip Fracture Score (AHFS) was developed recently and showed promising results. Until now, this tool has not been validated; therefore, we aim to perform an external validation of the AHFS. Methods On admission, AHFS variables were prospectively collected. The prospectively collected data were used retrospectively to externally validate the AHFS in a cohort of hip fracture patients that were admitted to a hospital in Delft (Delft cohort). The AHFS score was retrospectively calculated for all hip fracture patients meeting the inclusion criteria. The characteristics of the Delft Cohort, AHFS score, sensitivity, specificity, positive predictive value, negative predictive value, and area under the curve were calculated and compared to the original Almelo cohort, in which the AHFS was developed. Results 422 patients of 70 years and older were included. Mortality within 30 days was 7.6% and similar to the 7.5% observed in the Almelo cohort. For the high-risk cut-off point, specificity was 95.4% in the Delft Cohort vs. 92.5% in the Almelo Cohort, and sensitivity for the low-risk cut-off point was 75.9 vs. 78.1% in the Almelo Cohort. The area under the ROC curve was 0.70 (95% CI 0.60-0.79) compared to 0.82 in the Almelo cohort. Conclusions The validity of the score was acceptable and comparable to the values in the Almelo cohort. This score might be used to identify patients at high risk for early mortality.