2025 Southeastern Residency Conference

Title: Assessing the Utility of Enoxaparin Anti-Xa Monitoring in Obesity for Venous Thromboembolism (VTE) 
Prophylaxis on Clinical Outcomes in the Hospital Setting 
Authors: Emilee Byrd, Angelica Marques, Ann Maxwell 
Background: Anti-Xa monitoring has been suggested to assess enoxaparin dosing in certain patient populations for the treatment of venous thromboembolism (VTE). However, there is no clear guidance on goal ranges for prophylactic enoxaparin and how this can affect the bleeding or clotting risk. Morbid obesity (BMI >40 kg/m2) is an important factor that can increase the risk of VTE. Some institutions have adopted anti-Xa monitoring in this patient population to guide prophylactic dosing. The purpose of this research study is to assess the use of anti-Xa monitoring for VTE prophylaxis using enoxaparin in obesity and its impact on clinical outcomes.   
Methods: This is a retrospective, observational single center cohort study evaluating morbidly obese patients admitted to McLeod Regional Medical Center that received prophylactic dosing of enoxaparin between August 1, 2023 and July 31, 2024. In order to be included in the study, patients needed to be 18 years or older, have a BMI >40 kg/m2, receive at least three doses of enoxaparin, and have at least one anti-Xa level collected. Patients with acute kidney injury (AKI) within the last seven days, pediatric patients, pregnant patients, orthopedic surgery patients, and trauma patients will be excluded.  The primary outcome is a composite of any VTE and any bleeding during hospitalization following prophylactic enoxaparin initiation. Secondary outcomes will include the individual components of the primary outcome (VTE, bleeding), number of repeat anti-Xa levels, percentage of anti-Xa levels in goal range and percentage of anti-Xa levels drawn within an appropriate time frame.  
Results: A total of 218 patients with a BMI >40 kg/m2 and receiving enoxaparin for VTE prophylaxis were reviewed. After applying the exclusion criteria, 81 patients were included in the study.  
The median age of patients included was 58 [IQR 44,70] with normal renal function and a median BMI of 50 [IQR 44,58]. Of the 81 patients included, 11% were also on concomitant NSAIDs and 40% of patients were receiving concomitant antiplatelet therapy with the most common being aspirin.  
For the primary composite outcome there were no incidences found of VTE and any bleeding in the 81 patients included in the study. 79% of the 81 anti-Xa levels collected were within the appropriate time frame with 59% of those levels being within the goal range. The incidence of sub-therapeutic levels that were collected within the appropriate time frame was 27% and 14% for supra-therapeutic levels. 
Conclusions:  Dose adjusting enoxaparin for VTE prophylaxis in morbidly obese patients does not appear to increase bleeding or VTE events. Anti-Xa monitoring can for VTE prophylaxis can lead to wasted resources when levels are drawn inappropriately and also lead to additional blood draws from the patient to obtain the level within the time frame. Based on the findings from this study, in patients with stable renal function receiving BMI dosing of enoxaparin it is reasonable to not check anti-Xa levels as this was not correlated with VTE or bleeding. Concomitant therapy with aspirin did not appear to increase the risk of bleeding.