Monitoring Unfractionated Heparin (UFH) therapy: which Anti-Factor Xa assay is appropriate?
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.
Ignjatovic
Vera
V
Department of Clinical Haematology, Royal Children's Hospital, Melbourne, Australia. verai@unimelb.edu.au
Summerhayes
Robyn
R
Gan
Andrew
A
Than
Jenny
J
Chan
Anthony
A
Cochrane
Andrew
A
Bennett
Martin
M
Horton
Stephen
S
Shann
Frank
F
Lane
Geoff
G
Ross-Smith
Maree
M
Monagle
Paul
P
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
D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006495:Heparin, Low-Molecular-Weight; D011933:Reagent Kits, Diagnostic