title: Interlaboratory agreement in the monitoring of unfractionated heparin using the anti-factor Xa-correlated activated partial thromboplastin time.
abstract: BACKGROUND
  In an effort to improve interlaboratory agreement in the monitoring of unfractionated heparin (UFH), the College of American Pathologists (CAP) recommends that the therapeutic range of the activated partial thromboplastin time (APTT) be defined in each laboratory through correlation with a direct measure of heparin activity such as the factor Xa inhibition assay. Whether and to what extent this approach enhances the interlaboratory agreement of UFH monitoring has not been reported.
  
  
  OBJECTIVE
  We conducted a cross-validation study among four CAP-accredited coagulation laboratories to compare the interlaboratory agreement of the anti-FXa-correlated APTT with that of the traditional 1.5-2.5 times the midpoint of normal (1.5-2.5:control) method for defining the therapeutic APTT range.
  
  
  METHODS
  APTT and FXa inhibition assays were performed in each laboratory on plasma samples from 44 inpatients receiving UFH.
  
  
  RESULTS
  Using the anti-FXa-correlation method, there was agreement among all four laboratories as to whether a sample was subtherapeutic, therapeutic or supratherapeutic in seven (16%) patient samples. In contrast, consensus was achieved in 23 (52%) samples when the 1.5-2.5:control method was employed.
  
  
  CONCLUSIONS
  The anti-FXa-correlation method does not appear to enhance interlaboratory agreement in UFH monitoring as compared with the traditional 1.5-2.5:control method. Adoption of the anti-FXa-correlation method produces considerable disparity in UFH dosing decisions among different centers, although the clinical impact of this disparity is not known.
authors.affiliation: Department of Medicine, University of Pennsylvania, Philadelphia, PA, USA. adam.cuker@uphs.upenn.edu
authors.forename: A
authors.initials: A
authors.lastname: Cuker
authors.forename: B
authors.initials: B
authors.lastname: Ptashkin
authors.forename: B A
authors.initials: BA
authors.lastname: Konkle
authors.forename: S W
authors.initials: SW
authors.lastname: Pipe
authors.forename: H C
authors.initials: HC
authors.lastname: Whinna
authors.forename: X L
authors.initials: XL
authors.lastname: Zheng
authors.forename: D B
authors.initials: DB
authors.lastname: Cines
authors.forename: E S
authors.initials: ES
authors.lastname: Pollak
mesh_terms: D000925:Anticoagulants / Q000493:pharmacokinetics; D019411:Clinical Laboratory Techniques / Q000592:standards; D016903:Drug Monitoring / Q000379:methods* / Q000592:standards; D065427:Factor Xa Inhibitors; D006493:Heparin; D006801:Humans; D015588:Observer Variation; D010314:Partial Thromboplastin Time / Q000592:standards*; D017410:Practice Guidelines as Topic; D012016:Reference Values
chemical_list: D000925:Anticoagulants; D065427:Factor Xa Inhibitors; D006493:Heparin