The anti-Xa assay
is an automated ready-to-use, calibrated chromogenic assay, which works by adding a citrated patient plasma sample to a mixture of buffer, chromogenic substrate, and excess factor Xa.
Among its disadvantages, anti-Xa assay
does not reflect all the anticoagulant properties of UFH, including prothrombin, factors IX and VIII, and antithrombin activity (Price et al., 2013; Takemoto et al., 2013).
* Rivaroxaban: anti-Xa assay
utilising a specific rivaroxaban calibrator
Fully automated Anti-Xa assays
permit routine labs to easily monitor UFH.
INR responses vary widely depending on the thromboplastin assay reagent, but a calibrated anti-Xa assay
appears to be a suitable method for determination of Riva concentration (13-16).
* The anti-Xa assay
for enoxaparin and nadroparin is currently available from the Johannesburg Hospital Haematology Laboratory (011 488-3068 or 011 489-8552), as well as from most private laboratories.
Rivaroxaban has been shown to prolong the prothrombin time, (7,8) activated partial thromboplastin time, (9) and dilute Russell viper venom time (DRVVT) (10) in a concentration-dependent manner, but measuring drug activity by chromogenic anti-Xa assay
may be preferred.
(5) This article also includes a discussion of the preferred method of monitoring LMWH by chromogenic anti-Xa assay
. Then look at the Fritsma Factor website to view the question/answer discussion on antithrom-bin in the anti-Xa assay
(2,3) In order to prevent activation of the hemostatic system into the circuit, unfractionated heparin (UH) is usually administered for patients on ECMO and therapeutic anticoagulation is monitored by various laboratory tests: activated clotting time, activated partial thromboplastin time (aPTT), anti-Xa assay
, and thromboelastography.