Abstract
Introduction. Low molecular weight heparin (LMWH) is preferred for malignancy-associated venous thromboembolism (VTE). Many providers monitor LMWH with anti-Xa levels, despite little validation on correspondence with patient outcome. Methods. This is a retrospective, single institution study of anti-Xa measurement in malignancy-associated thrombosis. Cases were identified using the Electronic Data Warehouse, and inclusion was confirmed by two independent reviewers. Malignancy type, thrombotic history, measurement rationale and accuracy, clinical context, and management changes were evaluated. Results. 167 cases met inclusion criteria. There was no clear rationale for anti-Xa testing in 56%. Impaired renal function (10%), documented or suspected recurrent thrombosis despite anticoagulation (9%), and bleeding (6%) were the most common reasons for testing. Incorrect measurement occurred in 44%. Renal impairment was not a significant impetus for testing, as 70% had a GFR > 60. BMI > 30 was present in 40%, and 28% had a BMI < 25. Clinical impact was low, as only 11% of patients had management changes. Conclusions. Provider education in accuracy and rationale for anti-Xa testing is needed. Our study illustrates uncertainty of interpretation and clinical impact of routine anti-Xa testing, as management was affected in few patients. It is not yet clear in which clinical context providers should send anti-Xa levels.
Highlights
Low molecular weight heparin (LMWH) is preferred for malignancy-associated venous thromboembolism (VTE)
Since the CLOT study [1], low molecular weight heparin (LMWH) has been the preferred treatment for malignancyassociated venous thromboembolism (VTE) given its improved efficacy compared to warfarin
A recent study of malignancy associated VTE showed that rates of LMWH use increased from 18% in 2000 to 31% in 2007 [2]
Summary
Since the CLOT study [1], low molecular weight heparin (LMWH) has been the preferred treatment for malignancyassociated venous thromboembolism (VTE) given its improved efficacy compared to warfarin. A recent study of malignancy associated VTE showed that rates of LMWH use increased from 18% in 2000 to 31% in 2007 [2]. There is little clinical validation on how anti-Xa levels should be interpreted and how they correspond with patient outcome, if at all. There is no clear consensus on the therapeutic range for anti-Xa activity in patients receiving prophylactic or treatment doses of LMWH for either VTE or acute coronary syndrome indications [7]. The concern for a need to monitor often relates to uncertainty regarding how LMWH behaves in specific Thrombosis populations, those with renal insufficiency, extremes of body weight, and pregnancy. Despite improved outcomes over warfarin, patients with malignancyassociated VTE treated with LMWH still have a 9% risk of recurrent thrombosis at 6 months [1]. The goal was to evaluate whether the anti-Xa level was checked correctly, the impetus for checking the level, what portion of levels drawn were therapeutic, and whether results impacted management
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