Potential Inaccuracy of Point-of-Care INR in Dabigatran-Treated Patients

Abstract

Objective: To report 2 cases in which point-of-care international normalized ratios (INRs) in dabigatran-treated patients were inaccurate. Case Summary: A 59-year-old woman with paroxysmal atrial fibrillation was started on warfarin. After 3 days, warfarin was discontinued, and the decision was made to switch to dabigatran 150 mg twice a day, which was started 2 days after the warfarin was discontinued. As treatment was being converted from warfarin to dabigatran therapy, the woman's primary care physician referred her to our anticoagulation clinic, where her point-of-care INR was 7.2. A laboratory INR performed approximately 30 minutes later was 1.7. Several repeat point-of-care INRs were elevated and discordant with the laboratory INRs. A second patient, a 52-year-old man, was started on dabigatran after an ablation procedure, as a bridge to warfarin. Approximately 16 hours after a single dose of dabigatran etexilate 150 mg, the point-of-care INR was 1.6. Discussion: Dabigatran etexilate is an oral direct thrombin inhibitor that is approved for use in thromboprophylaxis of atrial fibrillation and deep vein thrombosis. Dabigatran's predictable pharmacokinetic profile allows for a fixed-dose regimen without the need for coagulation monitoring. In certain clinical situations (eg, switching treatment between dabigatran and warfarin), INR testing is performed as part of routine clinical care. During the development program for dabigatran, laboratory testing of INR was performed, with INRs at therapeutic concentrations of dabigatran ranging from 1.1 to 1.7. Supratherapeutic concentrations of dabigatran elevated the INR to slightly higher levels, between 1.7 and 2.4. Even at extremely high dabigatran concentrations, the INR was generally in the range of 2.3-3.5. Conclusions: We advocate laboratory INR testing with simultaneous assessment of the activated partial thromboplastin time in patients who are receiving or who have recently received dabigatran. A prospective evaluation assessing the accuracy of the commonly used point-of-care INR devices in patients receiving dabigatran would confirm our findings with respect to this device and determine whether our findings extend to other commonly used devices.