title: Wide variability in the sensitivity of APTT reagents for monitoring of heparin dosage.
abstract: OBJECTIVE
  To assess the sensitivity of activated partial thromboplastin time (APTT) reagents for monitoring heparin dosage using data from the UK National External Quality Assessment Scheme (NEQAS) for blood coagulation.
  
  
  METHODS
  Data were reviewed from four surveys using samples prepared by addition of heparin to normal plasma in vitro and from two surveys in which samples were prepared using plasma from patients receiving heparin therapy (ex vivo samples).
  
  
  RESULTS
  For both in vitro and ex vivo samples, notable differences between APTT reagents with respect to heparin sensitivity were noted. This indicates that a uniform therapeutic range of 1.5-2.5 calculated by the APTT ratio may not be appropriate for all reagents. Reagent sensitivity in ex vivo samples was substantially different to that in in vitro samples.
  
  
  CONCLUSIONS
  The results of this large series of laboratories clearly indicate that reagent specific therapeutic ranges may be necessary, and that samples prepared by the addition of heparin to normal plasma in vitro can be misleading and should not be used.
authors.affiliation: Royal Hallamshire Hospital, Sheffield.
authors.forename: S
authors.initials: S
authors.lastname: Kitchen
authors.forename: I
authors.initials: I
authors.lastname: Jennings
authors.forename: T A
authors.initials: TA
authors.lastname: Woods
authors.forename: F E
authors.initials: FE
authors.lastname: Preston
mesh_terms: D000208:Acute Disease; D000925:Anticoagulants / Q000097:blood*; D001779:Blood Coagulation Factors / Q000032:analysis; D004334:Drug Administration Schedule; D006493:Heparin / Q000008:administration & dosage / Q000097:blood*; D006801:Humans; D007202:Indicators and Reagents / Q000592:standards*; D010314:Partial Thromboplastin Time; D013923:Thromboembolism / Q000517:prevention & control*
chemical_list: D000925:Anticoagulants; D001779:Blood Coagulation Factors; D007202:Indicators and Reagents; D006493:Heparin