Low Molecular Weight Heparin Anti-Factor Xa Level Monitoring in a Healthcare System

Purpose: Low molecular weight heparin (LMWH) is widely used for the prevention and treatment of deep vein thrombosis and pulmonary embolism. Routine monitoring of therapeutic effects through anti-Xa levels is not recommended but may be beneficial in patients with altered pharmacokinetics including pregnancy, weight extremes, or renal impairment. Levels should be drawn approximately four hours after the third dose to measure peak anti-Xa activity after achieving steady state. Untimely monitoring results in excessive testing, increased laboratory costs, and unwarranted dose adjustments compromising patient safety and efficacy. The purpose of this performance improvement project was to evaluate the appropriateness of monitoring LMWH anti-Xa levels and identify opportunities to optimize ordering within a healthcare system.

Methods: A random sample, retrospective chart review of patients at a multi-site hospital system over a 3 year period was conducted. Inclusion criteria were adult inpatients with at least one anti-Xa level ordered. Data collection included the anticoagulant agent, dose, indication, and administration time; indication for anti-Xa level monitoring, and anti-Xa sample collection time relative to the dose of the anticoagulant administered. Data was collected to assess if the dose was appropriately adjusted in patients who received an anticoagulant dose adjustment following anti-Xa level monitoring. Baseline characteristics collected included patient's creatinine clearance (CrCl), weight, and COVID-19 status. Primary outcomes of this study consisted of ordering trends for anti-Xa levels including indication and corresponding dose adjustments. Secondary outcomes included anti-Xa levels ordered at the appropriate time window and incidence of bleeding or thrombosis following inappropriate dose adjustments.

Results: A total of 220 patients with anti-Xa level monitoring were reviewed. An appropriate indication for anti-Xa level monitoring was identified in 28% of patients. Of the 49 patients that warranted anticoagulant dose adjustments following anti-Xa levels, 45 patients (92%) received appropriate dose adjustments. Anti-Xa levels were drawn after the third therapeutic dose of LMWH in 146 patients and 84 of these patients had levels drawn 3-5 hours post-dose. Therefore, 54% of levels drawn were within the appropriate time frame. A total of 4 patients had documentation of bleeding and 1 patient had thrombosis following an inappropriate dose adjustment of LMWH.

Conclusion: Appropriate anti-Xa level monitoring in patients with altered pharmacokinetics resulted in justified LMWH dose adjustments and ensured therapeutic concentrations were attained. In patients who received appropriate monitoring and subsequent dose adjustments, there were no adverse events noted. The results of this performance improvement project will be reviewed with pertinent stakeholders and a multi-disciplinary approach will be utilized to develop a protocol for LMWH anti-Xa level monitoring.

No relevant conflicts of interest to declare.