Allogenic Red Blood Cell Transfusion Increases Risk of Overall Infection After Surgery for Spinal Metastasis: A Retrospective Multi-Institutional Cohort Study of 796 Patients

Background Spinal metastasis surgery can involve significant blood loss and subsequent allogenic red blood cell (RBC) transfusion use. Although transfusion has been linked with increased infection rates in other settings, evidence within spinal metastasis surgery is limited. This study aimed to (1) report the incidence of overall infection after surgery, (2) assess if transfusion and other clinical factors increase infection risk, and (3) explore if a safe transfusion dose exists. Methods Adults with spinal metastasis undergoing decompressive or stabilization surgery between 2017–2022 at two institutions in the United States and United Kingdom were retrospectively included. The primary outcome was overall infection 30 days postoperatively. Multivariable logistic regression assessed transfusion and other risk factors for infection. Additional confounders (anemia, operative time, hospital stay, blood loss) were included in a sensitivity analysis. Results Among 796 patients (mean age 62±12 years, 41% female), 127 (16%) developed infections. Transfusion was given in 329 (41%) of patients and was independently associated with increased risk of overall infection postoperatively (OR 2.28, p<0.001), which persisted in sensitivity analysis (p<0.012). A dose-dependent association was observed (250mL increase: OR 1.10, p=0.014) without safe threshold (1-unit: OR 2.11, p=0.030). Higher BMI, COPD, elevated white blood cell count, fast-growing primary tumor, ≥3 spinal metastases, ≥4 levels operated, low serum albumin, and preoperative chemo-, immuno- or targeted therapy were also associated with infection (p<0.05). Conclusions Spinal metastasis surgery carries high risk of both RBC transfusion and infection. Transfusion increased risk of infection in a dose-dependent manner without safe threshold. Although often unavoidable, surgeons should strive for restrictive transfusion strategies and optimize perioperative protocols to reduce transfusion requirements. Higher comorbidity and tumor burden, extensive surgical procedures, and preoperative chemo-, immune-, or targeted therapy further increased infection risk. These factors may aid in risk stratification and balancing the need for transfusion accordingly. Additionally, surgeons may decrease infection risk by improving nutritional status (BMI, albumin levels) and favoring less invasive procedures over extensive (blood loss-prone) surgery.