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Rivaroxaban Causes False LAC Positive

George reviewed this question posted to the American Society for Clinical Laboratory Science Consumer Web Forum: “After DVT/PE helped by TPA/heparin and now on Xarelto 4 weeks, my first blood draw shows factor VIII 228%, DRVVT screen 126 sec, confirmation 61 sec, normalized ratio 1.96, but hex phase phospholipid normal range and antiphospholipid normal range. Are any of these likely affected by clots still dissolving? Does any of this suggest longterm clotting disorder just manifesting now? All other reports normal except slightly elevated liver enzymes.”

George responds, from your laboratory results it appears that you may have been taking Xarelto (rivaroxaban) at the time your blood specimen was collected for the DRVVT and factor VIII assays. Xarelto is a relatively new anticoagulant and we are learning that it interferes with the results of many of our clot-based coagulation tests such as factor VIII and DRVVT. This is an innocent consequence of Xarelto’s anticoagulant properties that should not raise concern.
As evidence mounts, laboratory scientists recommend that physicians order clot-based coagulation assays such as prothrombin time/international normalized ratio (PT/INR), partial thromboplastin time (PTT or APTT), lupus anticoagulant testing such as DRVVT and hex-phase, and factor assays at least one week after Xarelto therapy is discontinued. Conversely, the antiphospholipid tests, which usually include the anti-beta-2-glycoprotein 1 antibody and anti-cardiolipin antibody tests are reliable during Xarelto therapy, as they are performed using non-clot-based technology.
Your physician is likely to order repeat laboratory tests after your Xarelto therapy is discontinued or after a 12-week interval subsequent to your previous tests, and it is likely the DRVVT and factor VIII results may return to normal.

Comments (1)
Anticoagulant Therapy
Aug 29, 2016 5:40pm

While FVIII might return to
While FVIII might return to normal range after Xarelto discontinuation, FVIII activity by the clotting one-stage assay was rather underestimated in DVT patients from a mean of 190 (171–208) to 137 IU/dL (121–154), Also in donors who showed a FVIII decrease of 30–35 IU/dL on rivaroxaban. The chromogenic FVIII assay was also mildly affected:
Tichelaar V. et al. Interference of rivaroxaban in one-stage and chromogenic factor VIII:C assays. Thromb Haemost. 2011;106:990–2.

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