anti-Xa assay


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anti-Xa assay

A test that monitors blood clotting in patients taking anticoagulant drugs, such as low molecular weight heparin or unfractionated heparin. Heparins bind to antithrombin, which inhibits clotting factor Xa. The degree to which factor Xa is inhibited is measured by this assay.
See also: assay
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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.