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Monitoring IV Unfractionated Heparin with the PTT

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.

Comments (1)
Sep 7, 2011 5:15am

Thanks George. I got a call from a nurse yesterday regardin
Thanks George. I got a call from a nurse yesterday regarding this very topic. They may draw blood for heparin monitoring using aPTT one of several ways: 1. peripheral, 2. central line, 3. above or below infusion. She stated that depending on how blood is drawn, they get various results but are adjusting dose based on this. Are there recommendations out there for this type of draw? If peripheral stick is not possible, what are recommendations for drawing from a port? AND we always get this question. How long to turn off a heparin drip to draw heparin sensitive testing? Is there anything stated about that? Kim Kinney, Indiana University

Hi, Kim, thank you for your question. I had the opportunity to check references on these questions when Alexis Bennett and I wrote “Quick Guide to Venipuncture” in 2010 (AACC Press, note the self-promotion). Peripheral blood is the preferred specimen, and it should always be collected below the infusion or from the opposite limb, never above the infusion. When collecting from a vascular access device, discontinue the infusion for “several minutes,” disinfect the device, connect a matching syringe, and flush with 3-5 mL of saline. From some local protocols, I’ve seen three minutes as the time to stop the infusion. Then collect 3-5 mL of blood, discard, and proceed with the collection using a fresh syringe.
I don’t have a good answer to “how long to turn off a heparin drip to draw heparin sensitive testing.” In most instances, you would want the heparin administration to be in steady state while the blood is being collected. If you are collecting for a test that is affected by heparin, you may want to wait until the heparin is discontinued. I hope this helps. Geo.

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