title: Investigation of an anti-activated factor X (anti-Xa) assay for the quantification of enoxaparin in human plasma.
abstract: OBJECTIVE
  Enoxaparin is a low-molecular weight heparin (LMWH) widely used for the treatment of thrombosis and measured through a chromogenic assay (anti-Xa). The aim of this project was to investigate the impact of patient and sampling sources of variation on an anti-Xa assay for enoxaparin.
  
  
  METHODS
  COATEST was used in accordance with manufacturer's instructions. A standard curve of LMWH concentration (0.1-1.0 IU/ml) was prepared. The shelf-life and freeze-thaw stability of Xa over a 6-month period were investigated. The effects of blood sample haemolysis and plasma antithrombin-III (AT) concentration were examined.
  
  
  RESULTS
  The standard curve performed well with high accuracy (average bias of 8.1%) and precision (average CV of 2.8%). The shelf-life of Xa once reconstituted could be extended from 1 month to 4 months if aliquots were frozen at -20°C. Some loss of anti-Xa activity was observed on freeze-thawing (bias up to 25%). Haemolysis of 2.5% was found to interfere with the assay. AT level as low as 50% did not affect assay accuracy.
  
  
  CONCLUSIONS
  Xa standards when frozen immediately after reconstitution could be used for the following 4 months. Haemolysis interferes with the assay, but a 50% reduction in AT does not significantly affect the assay result.
authors.affiliation: School of Pharmacy, University of Otago, Dunedin, New Zealand.
authors.forename: Hesham S
authors.initials: HS
authors.lastname: Al-Sallami
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Medlicott
mesh_terms: D000925:Anticoagulants / Q000097:blood* / Q000627:therapeutic use; D000990:Antithrombin III / Q000378:metabolism; D017984:Enoxaparin / Q000097:blood* / Q000627:therapeutic use; D015951:Factor Xa / Q000378:metabolism*; D005615:Freezing; D006461:Hemolysis; D006801:Humans; D008297:Male; D013927:Thrombosis / Q000188:drug therapy*
chemical_list: D000925:Anticoagulants; D017984:Enoxaparin; D000990:Antithrombin III; D015951:Factor Xa
keywords: anti-Xa; chromogenic; dalteparin; enoxaparin; haemolysis