A Comparative Trial of Anti-Factor Xa Levels Versus the Activated Partial Thromboplastin Time for Heparin Monitoring

Abstract

Objective: To determine if laboratory monitoring of intravenous (IV) unfractionated heparin (UFH) using an anti–activated factor X (anti–factor Xa) assay, as opposed to the activated partial thromboplastin time (aPTT), would result in a higher percentage of results within the goal range, fewer monitoring tests, and fewer dose adjustments. Methods: Retrospective, single-center, cohort study conducted at a community teaching hospital. A newly implemented deep vein thrombosis/pulmonary embolism treatment protocol, in which patients' doses of IV UFH were adjusted based on blood plasma anti–factor Xa level monitoring, was compared with a deep vein thrombosis/pulmonary embolism protocol, in which patients' IV UFH doses were adjusted based on monitoring with the blood plasma aPTT. We reviewed the medical records of 186 patients (88 managed by the anti–factor Xa assay–based protocol and 98 managed by the aPTT-based protocol) to determine how often monitoring tests were within the goal range (aPTT, 75–110 sec; anti–factor Xa, 0.3–0.7 U/mL), in addition to how many UFH dose adjustments and monitoring tests were required for each patient within a 24-hour period. Results: In patients undergoing IV UFH therapy whose blood plasma was monitored with anti–factor Xa assay levels, as opposed to the aPTT, there was a higher percentage of UFH test results within the goal range (69% vs 41%; P < 0.0001), fewer monitoring tests were needed (2.08 vs 2.73; P = 0.001), and fewer dose adjustments were required per 24-hour period (0.62 vs 1.47; P < 0.0001). Conclusions: Use of an anti–factor Xa assay–based UFH-monitoring protocol resulted in a higher percentage of within-range blood plasma heparin monitoring tests, fewer monitoring tests for the patient to achieve blood plasma monitoring tests within goal range, and fewer dose adjustments compared with a protocol based on blood plasma monitoring using the aPTT.

Keywords:

• unfractionated heparin
• factor Xa
• partial thromboblastin time
• dose adjustment
• pulmonary embolism