Supraprophylactic Anti–Factor Xa Levels Are Associated with Major Bleeding in Neurosurgery Patients Receiving Prophylactic Enoxaparin

Abstract

Prior studies demonstrated reduced risk for venous thromboembolism (VTE) in neurosurgical patients secondary to prophylaxis with both heparin and low-molecular-weight heparin. The ability to monitor low-molecular-weight heparin by obtaining anti-factor Xa (anti-Xa) serum levels provides an opportunity to evaluate safety and efficacy. The aim of this study was to describe characteristics of patients who have anti-Xa levels outside of the goal range (0.2-0.4/0.5 IU/mL) and investigate incidence of major bleeding and VTE. A single-center, retrospective, observational study was conducted on neurosurgical patients receiving enoxaparin for VTE prophylaxis between August 2019 and December 2020. Significance testing was conducted via Fisher exact test and independent samples t test. The study included 85 patients. Patients were less likely to have an anti-Xa level in the goal range if they were male, had a higher weight, or were morbidly obese. Three neuroendovascular patients (3.5%) experienced a major bleed. Serum anti-Xa levels were significantly higher in patients who experienced major bleeds compared with patients who did not (0.45 ± 0.16 IU/mL vs. 0.28 ± 0.09 IU/mL, P= 0.003). Patients with a supraprophylactic anti-Xa level (>0.5 IU/mL) were more likely to experience a major bleed (P= 0.005). One VTE event occurred: the patient experienced a pulmonary embolism with anti-Xa level at goal. Anti-Xa-guided enoxaparin dosing for VTE prophylaxis in neurosurgical patients may help prevent major bleeding. These data suggest that a higher anti-Xa level may predispose patients to major bleeding. Further evaluation is needed to identify the goal anti-Xa level for VTE prophylaxis in this population.