Context.—

Assessing direct oral anticoagulant (DOAC) drug levels by reliable laboratory assays is necessary in a number of clinical scenarios.

Objective.—

To evaluate the performance of DOAC-specific assays for various concentrations of dabigatran and rivaroxaban, assess the interlaboratory variability in measurement of these DOACs, and investigate the responsiveness of the routine clotting assays to various concentrations of these oral anticoagulants.

Design.—

College of American Pathologists proficiency testing survey data from 2013 to 2016 were summarized and analyzed.

Results.—

For dabigatran, the interlaboratory coefficient of variation (CV) of ecarin chromogenic assay was broad (ranging from 7.5% to 29.1%, 6.3% to 15.5%, and 6.8% to 9.0% for 100-ng/mL, 200-ng/mL, and 400-ng/mL targeted drug concentrations, respectively). The CV for diluted thrombin time for dabigatran was better overall (ranging from 11.6% to 17.2%, 9.3% to 12.3, and 7.1% to 11.2% for 100 ng/mL, 200 ng/mL, and 400 ng/mL, respectively). The rivaroxaban-calibrated anti-Xa assay CVs also showed variability (ranging from 11.5% to 22.2%, 7.2% to 10.9%, and 6.4% to 8.1% for 50-ng/mL, 200-ng/mL, and 400-ng/mL targeted drug concentrations, respectively). The prothrombin time (PT) and activated partial thromboplastin time (aPTT) showed variable dose and reagent-dependent responsiveness to DOACs: PT was more responsive to rivaroxaban and aPTT to dabigatran. The undiluted thrombin time showed maximum prolongation across all 3 dabigatran concentrations, making it too sensitive for drug-level monitoring, but supporting its use as a qualitative screening assay.

Conclusions.—

DOAC-specific assays performed reasonably well. While PT and aPTT cannot be used safely to determine DOAC degree of anticoagulation, a normal thrombin time excludes the presence of dabigatran.

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Author notes

Pham is a speaker for Alexion Pharmaceuticals and a consultant for Scientific Genzyme. Higgins served on the Clinical Care Improvement Steering Committee for Diagnostica Stago, Inc, and received honoraria for consultancy. Volod served on the Clinical Care Improvement Steering Committee for Diagnostica Stago, Inc, and received honoraria for consultancy. Wool served on the Clinical Care Improvement Steering Committee for Diagnostica Stago, Inc, and received honoraria for consultancy. The other authors have no relevant financial interest in the products or companies described in this article.

All authors are current or past members of the College of American Pathologists Hemostasis and Thrombosis Committee. Long is an employee of the College of American Pathologists.