Use of a Fixed Activated Partial Thromboplastin Time Ratio to Establish a Therapeutic Range for Unfractionated Heparin

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Abstract
ALTHOUGH THE use of low-molecular-weight heparin is increasing, unfractionated heparin is still widely used to treat venous and arterial thromboembolic disorders. Because the anticoagulant response to unfractionated heparin varies among patients1-4 and its efficacy and safety are thought to be optimal when a target therapeutic range is achieved,5-8 laboratory monitoring with dose adjustment is necessary to ensure that an appropriate level of anticoagulation is given. The activated partial thromboplastin time (aPTT), a clotting assay that reflects the ability of the heparin-antithrombin complex to inactivate thrombin, factor Xa, and other coagulation enzymes within the intrinsic pathway, is the most widely used laboratory test for monitoring heparin therapy9 because it is widely available, rapid, easily automated, simple to perform, and relatively inexpensive.