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June 2011 Quick Question: Antithrombotics

Here’s a summary of our June, 2011 Quick Question:

Which antithrombotic monitoring problem happens the most often in your laboratory?
a. Unexplained INR variation: 14 (29%0
b. Trouble correlating lab INR with POC INR: 4 (8%)
c. Heparin; is it UFH, LWMH, or pentasaccharide: 7 (14%)
d. Need a way to monitor antithrombins like argatroban: 16 (33%)
e. Need a way to monitor direct anti-Xa like rivaroxaban: 8 (16%)
To generalize from these results, INR variation continues to create difficulties that may be related to treatment and diet or inter-laboratory variation, though it is nice to see that we don’t have a lot of trouble correlating lab to point-of-care instrument results. With the advent of new oral anticoagulants, perhaps INR-related issues may begin to fade as we begin switching over.

A rising issue asks how to monitor our newly released oral anticoagulants dabigatran (Pradaxa) and rivaroxaban (Xarelto), both now cleared in Europe, Canada, and the US. Dabigatran is a direct thrombin inhibitor, rivaroxaban a direct anti-Xa inhibitor. Though manufacturers claim the new anticoagulants require no monitoring, in fact, physicians are already asking laboratories to monitor for compliance, to determine the cause of emergent bleeding, to monitor potential overdose, to learn anticoagulant effects in co-medication, for bridging between anticoagulants, in renal or liver disease, in people who weigh over 150 kg and have a proportionally reduced fluid compartment, in children or small adults who weigh less than 40 kg with proportionally increased fluid compartments, or in those with unstable hemostasis, such as pregnancy, malignancy, or chronic disseminated intravascular coagulation.

If you can excuse my self-promotion, I prepared a presentation for LABCON, given June 9 in Halifax, Nova Scotia, entitled, “Whatever Happened to the PT and PTT?” that addresses these issues and provides recommendations for assays now under development. Please click on the link and scroll to the bottom if you would a copy of the handout.

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