![]() ![]() The anti-Xa assay is a more direct measure of plasma heparin concentrations, and is reported in international units (IU) per mL. Because of this variability, each institution is required to establish its own therapeutic aPTT range, which often ranges from 1.5 to 2.5 times the normal value. In fact, only approximately half of the variability in aPTT results is explained by the heparin plasma concentration. These include timing and site of blood collection, lot-to-lot variability in reagents, and biologic influences on UFH pharmacokinetics and activity (eg, obesity and lupus anticoagulant). However, it is susceptible to numerous variables that may affect its accuracy. 6 The aPTT assay historically has been widely used because it is readily available, easy to perform, and is inexpensive. 4,6,12 The aPTT generally measures the intrinsic and common coagulation pathways, and reports the amount of time in seconds that is required for a clot to form in plasma after activation of the intrinsic pathway. Monitoring of anticoagulation with UFH most commonly utilizes aPTT or anti-Xa assays. Laboratory considerations related to OFXais This document reviews available literature on monitoring of UFH in patients transitioning from OFXais. 8-11 Despite guidance being available for monitoring the transition from DOAC to warfarin, for example, no such guidance is available for monitoring the transition to UFH. 7 Generally, package inserts of OFXais recommend that a transition to a parenteral alternative should dose the parenteral agent at the time the next oral dose is due. Many recommendations are available regarding transitions between DOACs and different anticoagulants, including the transition to UFH. 5 This situation is becoming frequent because of the increasing preference for use of DOACs over warfarin and of the anti-Xa assay over the aPTT assay. This may result in inaccurate measurement of UFH-specific anticoagulation. 4 Some DOACs, specifically the oral factor Xa inhibitors (OFXais), may cause problems when monitoring UFH via anti-Xa assays because their effects may linger throughout the initial period of UFH treatment. 3Ĭommonly used laboratory assays to monitor anticoagulation with UFH include activated partial thromboplastin time (aPTT) and anti-Xa assays. 2 However, many situations may warrant transition from a DOAC to a shorter-acting parenteral anticoagulant, such as unfractionated heparin (UFH), for reasons including acute kidney injury, inability to take oral medications, and surgical procedures. ![]() 1 The DOACs have gained widespread use because of their similar or superior efficacy, more predictable pharmacokinetics, and lesser need for monitoring compared with warfarin, the previous gold standard oral anticoagulant. The direct oral anticoagulants (DOACs) include the direct thrombin inhibitor dabigatran and the factor Xa inhibitors apixaban, rivaroxaban, edoxaban, and betrixaban. ![]()
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