Background: Current recommendations suggest investigation of heritable thrombophilia should not be carried out on patients receiving anticoagulation. However, information about the effects of direct oral anticoagulants (DOACs) on thrombophilia screening tests is useful, as clinical information is not always available when samples are received in the laboratory.

Aims: To investigate effects of rivaroxaban on a wide range of methods used in thrombophilia screening.

Methods: A sample from a patient with protein S deficiency and taking rivaroxaban (level 93ng/ml) was sent to UK NEQAS laboratories for thrombophilia testing, without relevant clinical information. Participants were asked to perform (Protein C (PC), Protein S (PS), Antithrombin (AT) and activated protein C resistance (APCR)) on the sample and interpret their results.

Results: 347 centres returned results. Medians were calculated for all methods employed for each test. Clot-based PC activity assay results were significantly higher than chromogenic-based assay results (122.7u/dl vs 101.7u/dl, p< 0.001). Thrombin-based antithrombin assays gave lower results than Xa-based methods (96.0u/dl vs 107.0u/dl, p< 0.001). PS activity assay results were higher than free PS antigen results (24.4u/dl vs 11u/dl, p< 0.001). These differences were seen across the range of methods employed by participants, confirming the consistent effect of direct Xa inhibitors on these assays. Despite this, all centres performing a full thrombophilia screen obtained the correct interpretation of PS deficiency, although 3 additionally reported APC resistance.

Conclusions: Anticoagulation with DOACs is not reported to affect chromogenic PC assays or free PS assays, so false negative results are unlikely if these tests are employed in a thrombophilia screen, as they are by the large majority of UK NEQAS participants. However, AT assays may be affected by either thrombin- or Xa-based inhibitors dependent on the substrate used, and false positive results may arise in patients with mild AT deficiency – our data show both these methods are widely used.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/effects-of-rivaroxaban-on-thrombophilia-screening-tests-results-from-a-uk-neqas-blood-coagulation-exercise/