Hidden blood loss after proximal femur fractures fixation: analysis of the first three postoperative days and influence of anticoagulants

Abstract Purpose Hidden blood loss (HBL) is an underrecognized contributor to total perioperative blood loss after hip fracture surgery. This study aimed to quantify HBL during the first three postoperative days following proximal femur fracture fixation and to assess the impact of preoperative anticoagulant therapy on blood loss and transfusion requirements. Methods A retrospective cohort study was conducted including patients aged ≥ 65 years who underwent surgical fixation of proximal femur fractures at a level I trauma center between January 2020 and December 2022. Total blood loss was estimated from perioperative hemoglobin changes and calculated blood volume. Patients were stratified according to anticoagulant use, and logistic regression analysis was performed to identify independent predictors of increased blood loss. Results Among 260 patients analyzed, median total blood loss was 1184 ml, and 25% experienced losses exceeding 1675 ml. High blood loss correlated significantly with anticoagulant use, higher BMI, and longer operative time ( p < 0.001). In multivariate analysis, anticoagulant therapy (particularly direct oral anticoagulants) remained an independent predictor of high blood loss (OR 3.06; 95% CI 1.47–6.37; p = 0.003). Patients in the highest quartile required significantly more transfusions, though short-term mortality did not differ. Conclusion Hidden blood loss after proximal femur fracture surgery is frequent and clinically relevant. Anticoagulant use, elevated BMI, and prolonged operative duration independently increase bleeding risk. Awareness of these predictors may support optimized perioperative management and transfusion planning in elderly fracture patients.