Here are the responses to our August, 2017 Quck Question: "How do you assay for direct oral anti-Xa antithrombotics like rivaroxaban?"
A. Prothrombin time: 2 (3%)
B. Partial thromboplastin time: 2 (3%)
C. Chromogenic anti-Xa : 31 (48%)
D. Dilute Ruessell viper venom time: 1 (2%)
E. DOASENSE urine detection strip: 0
F. We don't assay direct oral anti-Xa antthrombotics 29 (45%)
It is encouraging to learn that many of us have begun assaying the direct oral anti-Xa antithrombotics using the chromogenic anti-Xa assay despite the US FDA 's failure to approve validated calibrators and controls. From anecdotes around the USA, George has learned the demand for assays is high, especially from emergency rooms and from physicians and surgeons planning interventions on anticoagulated patients. For those of us who choose not to offer an assay, it is likely we will be required to do so very soon, given physician demands. Although the prothrombin time is the only procedure currently approved, most of us realize PT measurements vary widely by reagent source and coagulometer. We also know the PTT is relatively insensitive to the anti-Xa DOAC class. The DOASENSE was just recently described at the 2017 ISTH meeting in Berlin, and so far has not seen clinical application. There have been several publications recommending the DRVVT , but so far it hasn't caught on. One or two respondents use the chromogenic anti-Xa heparin assay, established using unfractionated heparin-based or hybrid curves, as a qualitative assay, concluding that a result of 0 units rules out their presence. This may be a reasonable approach until FDA approval of caibrators triggers the use of quantitiave assays.