Clinical Practice Patterns of Anti-Xa Monitoring During Low Molecular Weight Heparin Therapy

Abstract

Introduction: Therapeutic low molecular weight heparin (LMWH) regimens were developed empirically based on patient weight and renal function without the need for laboratory monitoring. The role of anti-Xa monitoring for patients receiving LMWH has yet to be fully established and is routinely performed only in high risk patients. At our institution, guidelines for monitoring LMWH recommend drawing anti-Xa levels for patients with chronic kidney disease or those with obesity requiring long-term therapy. The purpose of this analysis was to evaluate compliance with institutional guidelines for monitoring anti-Xa levels for patients receiving LMWH, including indication for anti-Xa monitoring, timing of anti-Xa level in relation to drug administration, and follow up actions of providers in response to abnormal anti-Xa levels. Methods: We conducted a retrospective chart review of adult patients who received therapeutic LMWH (enoxaparin or dalteparin) and were ordered for an anti-Xa level between September 1, 2014 and July 1, 2015. Patients were excluded if they were ordered for an anti-Xa level while on a prophylactic dose of LMWH or while on a non-LMWH factor Xa inhibitor. Data collected included patient demographics, LMWH dose and indication, ordering service, presence of a Hematology consult, reason for anti-Xa monitoring, timing of the level after the previous LMWH dose, and provider response to the level. Results: One hundred patients met inclusion criteria, 99 of whom received enoxaparin. Venous thromboembolism was the most common reason for LMWH therapy (85%) followed by atrial fibrillation (11%). The most frequent doses of enoxaparin administered were 1 mg/kg every 12 hours (52%), 1 mg/kg every 24 hours (22%) and 1.5 mg/kg every 24 hours (21%). The most frequently specified indications for anti-Xa monitoring were renal dysfunction and acute kidney injury (30%), followed by abnormal body mass index (13%); no indication was specified by the prescriber or pharmacist in 36% of cases. Of the 100 anti-Xa levels in the study, 65 were drawn at the correct time (3-5 hours after the previous dose of enoxaparin); of the 35 drawn at an incorrect time, 33 had levels measured more than 5 hours after the previous enoxaparin dose. Fifty-four of the initial anti-Xa levels were not within the therapeutic range for the dosing interval of LMWH; of these, follow up action was taken for only 21 patients (39%), most frequently resulting in a dose increase or decrease. Conclusions: In clinical practice, the use of anti-Xa monitoring is inconsistent and commonly done without a documented need. The majority of anti-Xa levels at our institution are drawn at the appropriate time after the previous dose of LMWH, but action is generally not taken in response to non-therapeutic levels. Additional guidance on the use of LMWH monitoring is needed. Disclosures No relevant conflicts of interest to declare.

Evaluation of anticoagulant monitoring in pediatric patients receiving enoxaparin for venous thrombosis treatment

“…Further prospective studies are warranted to better risk stratify which children require the multiple anti-Xa levels currently checked on all patients. We believe there is clinical equipoise to conduct a prospective study comparing the methods of checking 2 levels (before the 3 th dose and then at one week) versus checking our current standard 4 levels, which in the end becomes an average of 7.5 levels checked for 2 dose changes for a [6][7][8][9][10][11][12] week treatment course.…”

“…Traditionally in adult patients, anti-Xa monitoring is not routinely performed, mainly due to a potential of incorrectly drawing the levels and pharmacokinetic and pharmacodynamic stability in adult patients. [5][6][7] Monitoring may prove to be beneficial in adults if they have renal dysfunction or obesity.…”