Interpretation of Point-of-care INR Results in Patients Treated with Dabigatran

Abstract

BackgroundPoint-of-care devices for measurement of the international normalized ratio (INR) are commonly used to monitor therapy and maintain therapeutic levels of anticoagulation in patients treated with vitamin K antagonists. Dabigatran, a new oral, reversible direct thrombin inhibitor approved for stroke prevention in patients with atrial fibrillation does not require routine coagulation monitoring. However, case reports have identified falsely elevated point-of-care INR levels in patients treated with dabigatran using one of these devices (Hemochron). This in vitro study was designed to verify this issue. MethodsWe compared INR levels in whole blood and plasma using a Hemochron Jr. Signature+ point-of-care device (International Technidyne Corporation, Edison, NJ) with routine laboratory monitoring, using blood from healthy volunteers that was spiked with increasing concentrations of dabigatran. ResultsProthrombin time and INR levels were increased about 2- to 4-fold with the point-of-care device compared with laboratory measures across the plasma dabigatran concentration range 50-1400 ng/mL. At plasma concentrations of dabigatran likely to be observed in patients, at a dose of 150 mg twice daily (60-275 ng/mL), whole blood point-of-care INR values increased from 1.7 to 4.0, versus 1.1 to 1.5 measured with the laboratory coagulometer. Similar differences in prothrombin time were observed in plasma samples. ConclusionsINR levels in patients taking dabigatran are substantially higher using a Hemochron Jr. point-of-care device compared with laboratory values. We discourage the use of these devices specifically, as well as the use of the INR in general, for measuring the anticoagulant effect of dabigatran.