(441) Use of Dilute Thrombin Time for Direct Thrombin Inhibitor Monitoring at an Academic Medical Center

Introduction: Argatroban and bivalirudin are intravenous direct thrombin inhibitors (DTIs) utilized in patients when therapeutic anticoagulation with heparin products is contraindicated or ineffective, such as heparin-induced thrombocytopenia or heparin resistance. DTIs are routinely titrated to activated partial thromboplastin time (aPTT), but there are clinical scenarios in which the aPTT may be elevated prior to initiating anticoagulation in critically ill patients, thus making the use of standard aPTT goals suboptimal. Dilute thrombin times (dTT) are an alternative method of monitoring DTIs in patients with prolonged aPTTs. The purpose of this study was to assess utilization of dTTs at a large academic medical center.

Methods: This study was a retrospective chart review at a single academic medical center. Patients were included if they had at least one dTT and aPTT result while on a DTI. The primary outcome was the incidence of utilizing an individualized custom aPTT goal based on the dTT to aPTT correlation. Secondary outcomes included indication for dTT check and correlation between dTT and aPTT over time.

Results: A total of 31 patients were included and analyzed. The average age was 54 years old and 18 (58%) were male. Custom aPTT goals were utilized for 16 (52%) patients based on dTT to aPTT correlations. Indications for dTT checks were known lupus anticoagulant in 7 (23%) patients and concern for unreliable aPTT in 24 (77%) patients. Suspicions for unreliable aPTT were primarily due to concerns for synthetic clotting factor dysfunction or clot formation and/or progression with a therapeutic aPTT. Correlation between dTT and aPTT increased over time, producing a r2 value of 0.2 on first correlation and 0.8 by the fifth check.

Conclusions: Critically ill patients may present with elevated baseline aPTTs for numerous reasons, such as clotting factor abnormalities, presence of antiphospholipid antibodies, and presence of direct oral anticoagulants. Targeting the standard aPTT goal to monitor DTIs in these patients may result in subtherapeutic levels of anticoagulation. Utilizing the dTT to create custom aPTT goals and titrations for patients presenting with elevated aPTTs at baseline appears to provide adequate levels of anticoagulation with minimal safety concerns.