On the other hand, the same authors found a behavior for the CT parameter similar to that of our findings, using two different types of reagents (Extem and Intem) versus plasma concentration, as determined by the anti-Xa assay
. Evidence of a significant correlation between drug concentration and thromboelastometric parameters (CT, CFT, alpha angle, A5, and A10) was observed only after rivaroxaban administration (peak).
Of the DOAC assays in development, the chromogenic anti-Xa assay
is of strong interest for accurate and precise measurement of all "xabans."
As an added precaution, an anti-Xa assay
could be performed to confirm that supratherapeutic rivaroxaban levels are not present, because this study included high-therapeutic specimens up to 349 ng/mL rivaroxaban (anti-Xa 1.51 U/ mL by a low-molecular weight heparin curve), but supratherapeutic specimens were not encountered (Note added in proof: While the manuscript was in press, we encountered 2 patients heterozygous for factor V Leiden with supratherapeutic rivaroxaban concentrations of 590 ng/mL and 401 ng/mL [anti-Xa 2.48 [micro]/mL and 1.72 [micro]/mL by a LMWH curve, respectively].
Advantages of the anti-Xa assay
include achievement of therapeutic goal within 24 hours or less, fewer dosage adjustments and laboratory tests reducing the potential for titration errors, and saved nursing time (Fruge & Lee, 2015).
* Evaluate the local utility and practicality of validating currently available methods to quantify the anticoagulant activity of DTI (dilute thrombin time or ecarin time calibrated with dabigatran) and DFXaI (chromogenic anti-Xa assay
calibrated with rivaroxaban or apixaban).
* The anti-Xa assay
is currently available for enoxaparin and nadroparin at the Charlotte Maxeke Johannesburg Hospital NHLS haematology laboratory ((011) 488-3068 or (011) 489-8534) as well as in private laboratories.
Third, Anti-Xa assay
should be obtained in order to monitor danaparoid sodium.
LMWH levels cannot be monitored by the aPTT, but require a specialised anti-Xa assay
, which is currently available at Johannesburg Hospital Haematology Laboratory (tel (011) 488-3068).
Using an Anti-Xa assay
to monitor UFH has reduced blood transfusions by 4.7 percent for VTE patients, 8.2 percent for ischemic stroke patients, and 17.5 percent for acute coronary syndrome patients versus aPTT monitoring.