title: Antifactor Xa levels vs. activated partial thromboplastin time for monitoring unfractionated heparin. A pilot study.
abstract: OBJECTIVE
  The two most common methods for monitoring unfractionated heparin (UFH) infusion are the activated partial thromboplastin time (aPTT) and the antifactor Xa heparin assay (anti-Xa). The purpose of this study is to compare the performance of an aPTT protocol vs. an anti-Xa protocol in adult patients as defined by the time to reach therapeutic range, the percentage of time the values were within the goal range and the number of times laboratory monitoring was conducted. We then analysed the discordance between paired values of anti-Xa and aPTT.
  
  
  METHODS
  This was a single-centre prospective cohort pilot study conducted from 1 September 2013 to 31 May 2014.
  
  
  RESULTS
  Eighty-five patients were treated with UFH infusion, aPTT monitoring (n = 48), anti-Xa monitoring (n = 37). The number of times aPTT and anti-Xa values were ordered was (median, IQR) 14 (2-34) vs 7 (2-76); P = 0·23. The time to reach therapeutic range in hours was (mean, SD) 22 (20) aPTT vs 15 (13) anti-Xa; P = 0·08. Therapeutic range (>50-100% of the time) was achieved in only 5 (10%) patients in the aPTT group vs. 21 (57%) in the anti-Xa group; P < 0·01. Supratherapeutic values (>50-100%) were observed in 38 (78%) patients in the aPTT group vs. 14 (38%) in the anti-Xa group; P < 0·01. The discordance between aPTT and anti-Xa was evaluated using 234 paired values from 37 patients. There was discordance between anti-Xa and aPTT values 57% of the time. Two patients had bleeding complications requiring blood transfusion or discontinuation of post-pilot protocol.
  
  
  CONCLUSIONS
  Utilizing an anti-Xa protocol to monitor heparin infusion showed favourable results compared with utilizing an aPTT protocol by maintaining values within the therapeutic goal range. The most common discordant pattern in our study was a disproportionate prolongation of aPTT to anti-Xa values. Patients with discordant values presenting with high aPTT to normal anti-Xa values may have an increased risk of bleeding complications.
authors.affiliation: Department of Pharmacy, Memorial Hermann - Texas Medical Center, Houston, TX, USA.
authors.forename: S
authors.initials: S
authors.lastname: Samuel
authors.affiliation: Department of Pharmacy, Memorial Hermann - Texas Medical Center, Houston, TX, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Allison
authors.affiliation: Department of Pharmacy, Memorial Hermann - Texas Medical Center, Houston, TX, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sharaf
authors.affiliation: Department of Pharmacy, Memorial Hermann - Texas Medical Center, Houston, TX, USA.
authors.forename: G
authors.initials: G
authors.lastname: Yau
authors.affiliation: Department of Pharmacy, Memorial Hermann - Texas Medical Center, Houston, TX, USA.
authors.forename: G
authors.initials: G
authors.lastname: Ranjbar
authors.affiliation: Department of Pharmacy, Memorial Hermann - Texas Medical Center, Houston, TX, USA.
authors.forename: N
authors.initials: N
authors.lastname: Mckaig
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of Texas Medical School at Houston, Houston, TX, USA.
authors.forename: A
authors.initials: A
authors.lastname: Nguyen
authors.affiliation: Department of Hematology, The University of Texas Medical School at Houston, Houston, TX, USA.
authors.forename: M
authors.initials: M
authors.lastname: Escobar
authors.affiliation: Department of Neurosurgery and Neurology, The University of Texas Medical School at Houston, Houston, TX, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Choi
mesh_terms: D000925:Anticoagulants / Q000627:therapeutic use; D016903:Drug Monitoring / Q000379:methods; D015951:Factor Xa / Q000378:metabolism*; D065427:Factor Xa Inhibitors / Q000627:therapeutic use*; D005260:Female; D006493:Heparin / Q000627:therapeutic use*; D006801:Humans; D007262:Infusions, Intravenous / Q000379:methods; D008297:Male; D008875:Middle Aged; D010314:Partial Thromboplastin Time / Q000379:methods; D010865:Pilot Projects; D011446:Prospective Studies
chemical_list: D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006493:Heparin; D015951:Factor Xa
keywords: activated partial thromboplastin time; anticoagulation; antifactor Xa heparin assay; heparin laboratory monitoring; unfractionated heparin; venous thromboembolism