title: Can an anti-Xa assay for low-molecular-weight heparin be used to assess the presence of rivaroxaban?
abstract: BACKGROUND
  Due to the convenience afforded by the lack of required laboratory monitoring, direct oral anticoagulants (DOACs) are increasingly used as alternatives to Vitamin-K antagonists for certain medical conditions. However, there are circumstances in which assessment of DOAC plasma concentrations may be helpful in guiding clinical decisions, including patients presenting with either bleeding or thrombosis, or patients requiring urgent invasive procedures. Evaluating the anticoagulant effects of DOACs is often difficult because of the limited availability of DOAC-specific assays in most laboratories.
  
  
  OBJECTIVE
  To evaluate the correlation between ex vivo plasma concentrations of rivaroxaban and a chromogenic anti-Xa assay for low-molecular-weight heparin (LMWH) routinely used in our coagulation laboratory.
  
  
  METHODS
  Twenty-nine blood samples from 20 patients anticoagulated with rivaroxaban (dose; 10-20 mg/day) were evaluated using an anti-Xa assay for LMWH and results were correlated with rivaroxaban plasma concentrations using a rivaroxaban specific assay.
  
  
  RESULTS
  A linear dose-dependent relationship was demonstrated between plasma concentrations of rivaroxaban and the chromogenic anti-Xa assay for LMWH (R2 = 0.92). PT and PTT demonstrated poor correlations (R2 = 0.03; and R2 = 0.01, respectively) with rivaroxaban plasma concentrations.
  
  
  CONCLUSIONS
  Findings from this study suggest that if specific assays for rivaroxaban are unavailable, then the chromogenic anti-Xa assay for LMWH may be useful for assessing the anticoagulant effects of rivaroxaban.
authors.affiliation: Department of Pathology, Division of Transfusion Medicine and Hemostasis, UT Southwestern Medical Center, Dallas, TX, United States. Electronic address: Sean.Yates@UTSouthwestern.edu.
authors.forename: Sean G
authors.initials: SG
authors.lastname: Yates
authors.affiliation: Department of Pathology, Division of Transfusion Medicine and Hemostasis, UT Southwestern Medical Center, Dallas, TX, United States.
authors.forename: Sabra
authors.initials: S
authors.lastname: Smith
authors.affiliation: Department of Pharmacology, UT Southwestern Medical Center, Dallas, TX, United States.
authors.forename: William
authors.initials: W
authors.lastname: Tharpe
authors.affiliation: Department of Internal Medicine, Division of Hematology and Oncology, UT Southwestern Medical Center, Dallas, TX, United States.
authors.forename: Yu-Min
authors.initials: YM
authors.lastname: Shen
authors.affiliation: Department of Pathology, Division of Transfusion Medicine and Hemostasis, UT Southwestern Medical Center, Dallas, TX, United States.
authors.forename: Ravi
authors.initials: R
authors.lastname: Sarode
mesh_terms: D000284:Administration, Oral; D001780:Blood Coagulation Tests / Q000379:methods; D015951:Factor Xa / Q000378:metabolism*; D065427:Factor Xa Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005260:Female; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology*; D006801:Humans; D008297:Male; D000069552:Rivaroxaban / Q000008:administration & dosage / Q000493:pharmacokinetics*
chemical_list: D065427:Factor Xa Inhibitors; D006495:Heparin, Low-Molecular-Weight; D000069552:Rivaroxaban; D015951:Factor Xa
keywords: Anti-Xa; Direct oral anticoagulants; Laboratory; Low-molecular weight heparin; Rivaroxaban