title: Activated protein C resistance determined with a thrombin generation-based test is associated with thrombotic events in patients with lupus anticoagulants.
abstract: BACKGROUND
  Several studies suggest that antiphospholipid antibodies interfere with the activity of activated protein C (APC). This acquired form of APC resistance has been proposed as a possible pathogenic mechanism underlying hypercoagulability associated with the antiphospholipid syndrome (APS).
  
  
  OBJECTIVE
  We wanted to investigate the inhibitory effect of recombinant APC (rAPC) on ex vivo thrombin generation in plasma and the modification of this effect by the presence of lupus anticoagulants (LA).
  
  
  METHODS
  We analyzed plasmas from 81 patients with LA (52 patients fulfilling the criteria for the APS) and 91 controls. Percent inhibition of the endogenous thrombin potential (ETP) as a parameter of APC sensitivity was determined in plasmas using a thrombin generation-based APC resistance test probed with rAPC. All results were normalized using pooled normal plasma (PNP) as a reference.
  
  
  RESULTS
  Normalized percent inhibition of ETP by APC was lower in patients with LA [61.4%, 95% confidence interval (CI) 45.8-74.5%] compared to controls (107.8%, 95% CI: 107.1-109.3%). In patients with LA and APS, median inhibition was lower than in patients with LA without APS (44.6%, 95% CI: 30.1-55.7% vs. 78.8%, 95% CI: 73.9-95.8%). This difference also persisted when patients on warfarin therapy were excluded from the APS subgroup.
  
  
  CONCLUSIONS
  APC resistance can be demonstrated with a thrombin generation-based test in a majority of patients with the LA laboratory phenotype. A history of thrombotic events in patients with LA is associated with a stronger resistance to the anticoagulant effect of APC.
authors.affiliation: Department of Hematology, Ullevål University Hospital, Faculty Division Ullevål University Hospital, University of Oslo, Oslo, Norway. sigurdli@ulrik.uio.no
authors.forename: S
authors.initials: S
authors.lastname: Liestøl
authors.forename: P M
authors.initials: PM
authors.lastname: Sandset
authors.forename: M-C
authors.initials: MC
authors.lastname: Mowinckel
authors.forename: F
authors.initials: F
authors.lastname: Wisløff
mesh_terms: D020016:Activated Protein C Resistance / Q000150:complications*; D000328:Adult; D016736:Antiphospholipid Syndrome / Q000150:complications*; D001780:Blood Coagulation Tests; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011486:Protein C / Q000494:pharmacology; D011994:Recombinant Proteins; D013917:Thrombin / Q000494:pharmacology*; D019851:Thrombophilia / Q000150:complications; D013927:Thrombosis / Q000209:etiology*; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D016682:Lupus Coagulation Inhibitor; D011486:Protein C; D011994:Recombinant Proteins; D014859:Warfarin; D013917:Thrombin