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Letter to the editor
Clinical utility of anti-Xa monitoring and differential sensitivity of prothrombin time assays: an illustrated case report
  1. Hein Than1,
  2. Joanna Bao Ern Loh2,
  3. Christina Lai Lin Sum3,
  4. Heng Joo Ng1
  1. 1Department of Haematology, Singapore General Hospital, Singapore, Singapore
  2. 2Department of Internal Medicine, Singapore General Hospital, Singapore, Singapore
  3. 3Department of Laboratory Medicine, Tan Tock Seng Hospital, Singapore, Singapore
  1. Correspondence to Dr Heng Joo Ng, Department of Haematology, Singapore General Hospital, Outram Road, Singapore 169608, Republic of Singapore; ng.heng.joo{at}

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Novel oral anticoagulants (NOACs) are designed to avoid the need for monitoring of drug levels in routine clinical use. This has not impeded the development of laboratory tests for monitoring drug levels, but their place in routine clinical use of NOACs is currently contentious. Laboratory kits are now commercially available for measuring anti-Xa activity in patients given rivaroxaban (Bayer Healthcare AG, Leverkusen, Germany), an anti-Xa inhibitor. Besides such specific assays, rivaroxaban also affects routine coagulation tests such as the prothrombin time (PT). This effect is however dependent on the type of thromboplastin used.1 We describe our experience recently where access to anti-Xa monitoring and the differential sensitivity of two prothrombin assays were used to manage a difficult situation.

A middle-aged woman with end-stage renal failure presented with deep vein thrombosis of the right lower limb. This occurred as a complication of heparin-induced thrombocytopenia (HIT) which developed 9 days after exposure to heparin used in haemodialysis and maintenance of patency of an internal jugular venous access catheter. HIT was suspected because of a precipitous drop in her platelet count from 177×109/L 3 days earlier to 61×109/L, together with the new onset of thrombosis. This was supported by a positive test result from the Asserachrom HPIA polyspecific antibody assay …

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  • Contributors HT contributed to the conception of the idea underlying the case report, and the analysis and interpretation of data based on previous clinical trials. JBEL contributed to the acquisition of data and drafting of the work. CLLS was instrumental to facilitating the laboratory assays needed. HJN contributed to the conception of the idea underlying the case report, the analysis and interpretation of data, drafting and revising it critically for important intellectual content. He is the guarantor of this case report's overall content. All authors have reviewed the final version of the case report, and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

  • Competing interests None.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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