Unfractionated heparin (UFH) is a parenteral anticoagulant that is widely used for preventing and treating thromboembolic disorders. Common indications for use in the critically ill patient include pulmonary embolism, deep vein thrombosis, acute coronary syndromes, and stroke prophylaxis secondary to atrial fibrillation. This agent is appealing, especially for inpatient use, because of its rapid onset, short half-life, lack of renal elimination, and availability of a reversal agent. In addition, its efficacy and toxicity can be monitored with a widely available laboratory test. Historically, UFH has been monitored with activated partial thromboplastin time (aPTT), but various drawbacks such as interpatient variability and reagent specificity have prompted the use of alternative assays, specifically the antifactor Xa assay. This Drug Update column reviews practical considerations for monitoring UFH and provides a summary of the associated primary literature and guideline recommendations.

Blood coagulation is defined as...

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