Change associated with enoxaparin prophylactic anti-Xa levels during prolonged hospitalization in trauma patients

The administration of optimized venous thromboembolism (VTE) prophylaxis is critical in trauma patients. Guidance thus far has focused on initial enoxaparin dose selection and anti-factor Xa (anti-Xa) level monitoring. The need for monitoring and titrating prophylaxis in high-risk patients requiring prolonged hospitalization remains unknown.

This was a retrospective, single-center, cohort study including patients admitted with traumatic injury between January 1, 2021, and November 1, 2025, receiving enoxaparin for chemoprophylaxis and requiring prolonged hospitalization (>14 days). The primary outcome characterized clinically significant change in enoxaparin anti-Xa levels between the first level resulting within prophylactic target range and a repeat level obtained at least 6 days later resulting outside of prophylactic target range. Secondary outcomes evaluated the incidence of thrombus and clinically significant bleeding during the index hospitalization.

Of 272 consecutive patients screened, 43 patients were included within the study period. The patient cohort exhibited a median Injury Severity Score (ISS) of 21 [13.5-27] on admission. A total of 46 repeat anti-Xa levels were obtained at least 6 days following the first anti-Xa level within prophylactic target range. Clinically significant change in repeat anti-Xa levels was observed in 12/46 (26%) instances. The majority of repeat anti-Xa levels resulted in subtherapeutic range (10/12, 83.3%). The incidence of thrombus occurred in 7/43 (16.3%) patients and clinically significant bleeding in 1/43 (2.3%) patients during the index hospitalization.

Approximately one-quarter of patients exhibited clinically significant change between the first anti-Xa level within prophylactic target range and repeat anti-Xa levels obtained at least 6 days later in this evaluation. Subsequent larger studies are necessary to validate these hypothesis generating findings.