title: Monitoring Unfractionated Heparin (UFH) therapy: which Anti-Factor Xa assay is appropriate?
abstract: BACKGROUND
  Anti-Factor Xa (Anti-Xa) assays specifically determine the anticoagulant activity of UFH by measuring the ability of heparin-bound Antithrombin (AT) to inhibit a single enzyme, Factor Xa (FXa). Recent improvements in the automation, cost-effectiveness and accessibility of the assay to clinicians, have resulted in the Anti-Xa assay becoming a part of daily clinical practice in many institutions.
  
  
  OBJECTIVE
  We hypothesized that different Anti-Xa assays have different applicability for use in clinical settings, depending on the amount of UFH administered. This was investigated in a tertiary paediatric institution.
  
  
  METHODS
  Samples were collected from children receiving Low-dose of UFH of at least 10 IU/kg/h, with or without a previous bolus of up to 25 IU/kg/h, within the previous 6 h in the PICU and HDU. High-dose UFH population consisted of children undergoing Cardiac Catheterization (CC), who received a bolus of UFH of 100 IU/kg body weight, 30 min prior to sampling.
  
  
  CONCLUSIONS
  The Anti-Xa activity for a given dose of UFH was found to vary significantly based on the Anti-Xa assay and the population being monitored. Our study suggests that the MODIFIED COMATIC Anti-Xa assay provides the best physiological measure of the UFH effect in children, as it does not introduce sources of error, such as exogenous AT, which may increase the measured ant Factor Xa activity, nor Dextran Sulphate which can displace plasma protein bound heparin and once again leading to falsely elevated assay results. Further studies that include assessment of clinical outcomes are required to confirm the applicability of use of this particular assay in monitoring UFH therapy.
authors.affiliation: Department of Clinical Haematology, Royal Children's Hospital, Melbourne, Australia. verai@unimelb.edu.au
authors.forename: Vera
authors.initials: V
authors.lastname: Ignjatovic
authors.forename: Robyn
authors.initials: R
authors.lastname: Summerhayes
authors.forename: Andrew
authors.initials: A
authors.lastname: Gan
authors.forename: Jenny
authors.initials: J
authors.lastname: Than
authors.forename: Anthony
authors.initials: A
authors.lastname: Chan
authors.forename: Andrew
authors.initials: A
authors.lastname: Cochrane
authors.forename: Martin
authors.initials: M
authors.lastname: Bennett
authors.forename: Stephen
authors.initials: S
authors.lastname: Horton
authors.forename: Frank
authors.initials: F
authors.lastname: Shann
authors.forename: Geoff
authors.initials: G
authors.lastname: Lane
authors.forename: Maree
authors.initials: M
authors.lastname: Ross-Smith
authors.forename: Paul
authors.initials: P
authors.lastname: Monagle
mesh_terms: D000925:Anticoagulants / Q000097:blood / Q000494:pharmacology / Q000627:therapeutic use*; D001780:Blood Coagulation Tests / Q000379:methods / Q000592:standards; D002648:Child; D002675:Child, Preschool; D004305:Dose-Response Relationship, Drug; D065427:Factor Xa Inhibitors; D005260:Female; D006495:Heparin, Low-Molecular-Weight / Q000097:blood / Q000494:pharmacology / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D011933:Reagent Kits, Diagnostic / Q000592:standards; D012680:Sensitivity and Specificity
chemical_list: D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006495:Heparin, Low-Molecular-Weight; D011933:Reagent Kits, Diagnostic