Association Between Admission Neutrophil Count and Preoperative Deep Vein Thrombosis Risk in Older Patients with Hip Fracture: A Retrospective Cohort Study

Objective: This study investigated the association between admission neutrophil count and the risk of preoperative deep vein thrombosis (DVT) in older patients with hip fractures. Methods: We conducted a retrospective cohort study of patients aged ≥65 years with hip fractures between January 2015 and September 2019. The primary outcome was the presence of preoperative DVT diagnosed by color Doppler ultrasonography. We used multivariable logistic regression models to assess the association. We examined nonlinearity using smooth curve fitting and threshold effect analysis. Results: Among the 1807 patients, 571 (31.6%) developed preoperative DVT. We identified a nonlinear relationship with a threshold effect. The inflection point for neutrophil count was 3.17 × 109/L. Below this threshold, no significant association with DVT risk was observed (OR = 1.90, 95% CI: 0.90–3.99, p = 0.092). Interestingly, above this threshold, each 1 × 109/L increase in neutrophil count was associated with 8% lower odds of preoperative DVT (OR = 0.92, 95% CI: 0.89–0.96, p < 0.001). Conclusions: In older hip fracture patients, admission neutrophil count exhibits a curvilinear association with preoperative DVT risk with a threshold effect at 3.17 × 109/L. This data-driven threshold finding is exploratory and hypothesis-generating. It may support subsequent external validation and mechanistic research.