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Dabigatran and the iSTAT

From “SwimRose:”

Hi George, We recently had a case in our ER of a stroke patient on Pradaxa giving an INR of 2.0 with ISTAT, but the main lab instrument, an IL ACL, gave 1.1. Please comment.

Hello, and thank you for your question, which drove me to an early-morning search of theAbbott Diagnostics site for information tying the iSTAT to Pradaxa (dabigatran, “dabi”) therapy. There is no information, perhaps because the iSTAT prothrombin time/international normalized ratio (PT/INR) cartridge is cleared only for warfarin monitoring. I turned to a presentation made at the Thrombosis and Hemostasis Summit of North America (THSNA), by Rajiv Pruthi, MBBS, Co-Director, Special Coagulation Laboratory at the Mayo Hemophilia Center in Rochester, MN. Based on case analysis, Dr. Pruthi asserts that the PT and PTT are prolonged by dabi, which is a direct thrombin inhibitor, but their degree of prolongation varies with reagent-instrument combinations and does not accurately reflect drug levels. He does not specifically address the iSTAT, but I suspect he’d be comfortable with generalizing his statement to include point of care instruments. One cannot compare dabi-affected INRs across platforms, nor can one use the INR to monitor dabi.

From several THSNA presentations, the thrombin clotting time (TCT, TT) is the current best way to check for dabi clearance, as small dabi levels significantly prolong the TT. A normal TT indicates complete dabi clearance. Several presenters mentioned the apparent validity of Hyphen’s newly developed Hemoclot Thrombin Inhibitors assay, currently awaiting FDA clearance, which may be used to monitor argatroban and bivalirudin as well as dabi. Likewise, Centerchem’s Pefakit PiCT, which can monitor all Xa inhibitors and direct thrombin inhibitors looks promising, as does Stago’s ecarin clotting time. All these tests await the FDA.

I hope this helps, and I invite comments from anyone who has seen the effects of dabi on point of care instruments, as I assume this will be a common occurrence.

Comments (1)
Anticoagulant Therapy
May 16, 2012 5:59am

From Dr. Pruthi, The degree of prolongation of INR (with poi
From Dr. Pruthi, The degree of prolongation of INR (with point of care devices, POC or venipuncture INRs) vary with reagent/instrument combination. Since initial case reports (DeRemer CE. Am J Med 2011; Baruch L Ann Pharmacother 2011;45:e40) demonstrating discrepancy between venipuncture INR and POC INR, van Rynn (Am J Med 2012;125:417) confirmed such a discrepancy in a small 4 volunteer subject study with POC INRs being disproportionately prolonged compared to venipuncture INR. Thus one needs to be cautious in interpreting POC INR in patients on dabigatran.

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