Evaluation of DOAC Interferences on Technoclot® PT Owren

L. Rosenmayr, L. Wagner, N. B. Binder (Vienna, Austria)

Laboratory tests
Date: 17.02.2017,
Time: 17:15 - 18:15

Objective: Prothrombin time (PT) is still the leading test for monitoring oral anticoagulation therapy. PT reagents are known to differ in their sensitivities to individual DOACs. In the Owren’s method the sample is assayed in a 1:10 dilution, whereas in Quick based method samples are assayed undiluted. On account of this difference in sample dilution the Owren PT is expected to be less sensitive to DOAC interferences. Aim of the study was to investigate the rate of interference of different DOACs used in clinical practice, with the PT determined with Technoclot® PT Owren automated.

Methods: PT were determined with Technoclot® PT Owren automated, a combined Prothombin Time reagent based on Owren’s method. To investigate the assay performance in the presence of interfering substances plasma samples were spiked with increasing amounts of indirect and direct oral anticoagulants and clotting time, % of normal and INR values were determined. The relevant concentration ranges of interfering substances were chosen from the calibration ranges for the respective anticoagulants. A deviation of up to 15% from the un-spiked sample was considered as acceptable.

Results: No interferences (deviation of <15%) on INR values were found for Rivaroxaban samples up to 200ng/mL and for Dabigatran samples up to 300ng/mL. Even at 433.3 ng/mL Rivaroxaban and at 503 ng/mL Dabigatran, the INR value was within the normal range. Orgaran and Arixtra showed no interference with the INR result up to 1.3ng/mL and up to 1.61µg/mL, respectively. The % of normal results showed a somewhat higher sensitivity to Rivaroxaban. Concentrations up to 145ng/mL were within the acceptance criteria of <15% deviation from initial value. No interference was found for LMWH up to 1.8IU/mL and UFH up to 1.2IU/mL.

Conclusion: Our results indicate that Technoclot® PT Owren automated is relatively insensitive to direct and indirect oral anticoagulants. For Rivaroxaban and Dabigatran the concentrations in which no interference was observed were close to the expected peak concentration.