From “Berrylane:” If a patient is on IV heparin and a partial thromboplastin time (PTT, APTT) is ordered, what is the correct procedure for the blood draw?
Hello, and thank you for your question. In accordance with Hirsh J, Bauer KA, Donati MB, et al. Parenteral anticoagulants. Chest 2008:133:141S–59S, dosing of unfractionated, standard IV heparin for venous thromboembolic disease therapy begins with an 80 unit/kg IV bolus, followed by a continuous infusion of 18 units/kg/hour until it is discontinued. When monitoring IV unfractionated heparin using the PTT, collect blood below the infusion site or from the arm opposite the infusion site at least 4–6 hours after the bolus, but not more than 24 hours after initiation. The target therapeutic range should be the PTT in seconds that corresponds to 0.3–0.7 anti-Xa chromogenic heparin units, and the heparin dosage should be adjusted to maintain a PTT result within the target range. Do not use 1.5–2.5 times the mean of the reference interval as the target range, the dosage will be too small, raising the risk of a secondary thrombotic event. For more detail, go to our audio module page and see module 20, Monitoring Anticoagulant Therapy, Part 1, also, module 26, Partial Thromboplastin Time Assay.
By the way, the American College of Chest Physicians is preparing to publish an update to the Antithrombotic and Thrombolytic Therapy Clinical Practice Guidelines later this year or early next, however I don’t anticipate there will be a change in unfractionated heparin therapy dosage or monitoring guidelines. Thanks again to “Berrylane.” Geo.