Comparing Anti–Factor Xa and Activated Partial Thromboplastin Levels for Monitoring Unfractionated Heparin

Abstract

Background: Lab tests such as activated partial thromboplastin time (aPTT) or anti–factor Xa (anti-Xa) levels are typically used to monitor intravenous unfractionated heparin (IV heparin), with recent evidence suggesting that anti-Xa levels may provide a more accurate measure of anticoagulation. Objective: The Lexington Veterans Affairs Health Care System transitioned from using aPTT to anti-Xa levels in January 2017. This study was conducted to evaluate the efficacy and safety of this change. Methods: This was a retrospective cohort study comparing all patients receiving IV heparin per protocol for at least 24 hours from August 1, 2016, to January 31, 2017 (aPTT group), and February 1, 2017, to July 31, 2017 (anti-Xa group). The primary objective was a comparison of IV heparin doses required to achieve goal range between the 2 cohorts. Secondary objectives included a comparison of time to therapeutic goal, percentage of time within goal range, number of rate changes until therapeutic goal, and adverse outcomes, such as number of bleeds. Results: A total of 155 patients were included in this study. Significantly higher IV heparin doses were required to achieve therapeutic goal in the anti-Xa group, despite significantly fewer IV heparin rate changes required. Anti-Xa monitoring was not associated with an increased risk of adverse events. Conclusion and Relevance: Significantly higher IV heparin doses were required to achieve therapeutic anti-Xa levels after transitioning from an aPTT-based protocol in the largely unstudied veteran population. However, the transition from aPTT to anti-Xa monitoring appears safe and efficacious in these patients.

Validation of high concentrated thrombin time assay for unfractionated heparin monitoring

“…Despite the growing use of anti-FXa assay, UFH therapy has been widely monitored by the aPTT assay because of its simplicity, lower cost, and widespread availability. [4][5][6][7] Nevertheless, the aPTT assay can be affected by various pre-analytical and analytical factors. [8][9][10][11][12][13] Several studies have reported the discordance of the results obtained from the aPTT and anti-FXa assays for UFH monitoring.…”

“…[8][9][10][11][12][13] Several studies have reported the discordance of the results obtained from the aPTT and anti-FXa assays for UFH monitoring. 6,7,12,13,15,16 In addition, the UFH-induced prolongation of aPTT is highly dependent on the reagent and analyzer used. In this study, we aimed to determine the optimal thrombin concentration used in the hcTT assay and establish the potential of using the assay for UFH monitoring.…”

“…Despite the growing use of anti‐FXa assay, UFH therapy has been widely monitored by the aPTT assay because of its simplicity, lower cost, and widespread availability 4–7 . Nevertheless, the aPTT assay can be affected by various pre‐analytical and analytical factors 8–13 .…”

“…The main laboratory assays for monitoring UFH therapy are activated partial thromboplastin time (aPTT) and the chromogenic anti-factor Xa (anti-FXa) assays. [4][5][6][7] The aPTT test is the most widely used method to monitor UFH treatment because the test is simple, relatively cheap, and widely available. However, inter-laboratory variation caused by a different aPTT reagent and analyzer has been noted for the aPTT assay.…”

Individual variation in unfractionated heparin dosing after pediatric cardiac surgery

“…Typically, each institution has its own protocol for providing optimal unfractionated heparin therapy to achieve the target activated partial thromboplastin time (APTT) or activated clotting time (ACT) when patients are receiving extracorporeal membrane oxygenation (ECMO). Although studies have shown that unfractionated heparin therapy is more strongly associated with anti-Xa activity, measurement of anti-Xa activity as a routine practice is not necessarily the standard of care due to lack of evidence 1 – 4 .…”