title: Validation of a novel tissue factor assay in experimental human endotoxemia.
abstract: BACKGROUND
  Nuclear factor kappa B (NF-kappa B) activation and tissue factor (TF) expression may contribute to lethality in sepsis. Inappropriate in vivo expression of TF is likely responsible for fibrin deposition in sepsis-associated disseminated intravascular coagulation (DIC). Clinical assessment of TF expression has remained a major challenge. No point-of-care assays are currently available to measure the level of TF activity in whole blood. The current study examined the suitability of the TiFaCT assay as a point-of-care assay to detect TF expression.
  
  
  METHODS
  30 healthy male volunteers received 2 ng/kg of LPS. Tissue factor-dependent coagulation was quantified with a novel assay called tissue factor clotting time (TiFaCT), and by measurement of activation markers of downstream coagulation.
  
  
  RESULTS
  Ex vivo addition of anti-TF antibodies to blood slightly increased clotting times at 0-24 h (p<0.01) indicating that some tissue factor activity was present in whole blood at any time. LPS bolus infusion decreased TiFaCT clotting time by -23% compared to baseline (p<0.01), when in vivo clotting increased, as demonstrated by a 10-fold increase in prothrombin fragment levels (F1+2). Ex vivo incubation with LPS considerably shortened TiFaCT (from 1000s to 400s as compared to control incubation; p<0.01). This effect was blunted at 2-4 h after LPS infusion (i.e. the time of monocytopenia), but twofold enhanced 24 h after LPS challenge (p<0.01).
  
  
  CONCLUSIONS
  In summary, the TiFaCT assay was validated in our in vivo model of LPS-induced coagulation. It detected minute quantities of circulating TF even at baseline. TiFaCT is shortened at times of in vivo thrombin generation.
authors.affiliation: Department of Clinical Pharmacology, School of Medicine and Institute for Medical and Chemical Laboratory Diagnostics, Vienna University, Waehringer Guertel 18-20, A-1090 Vienna, Austria.
authors.forename: Claudia
authors.initials: C
authors.lastname: Marsik
authors.forename: Peter
authors.initials: P
authors.lastname: Quehenberger
authors.forename: Nigel
authors.initials: N
authors.lastname: Mackman
authors.forename: Bjarne
authors.initials: B
authors.lastname: Osterud
authors.forename: Thomas
authors.initials: T
authors.lastname: Luther
authors.forename: Bernd
authors.initials: B
authors.lastname: Jilma
mesh_terms: D000328:Adult; D001774:Blood Chemical Analysis / Q000379:methods*; D001780:Blood Coagulation Tests / Q000379:methods*; D019446:Endotoxemia / Q000097:blood* / Q000139:chemically induced; D004731:Endotoxins; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013925:Thromboplastin / Q000032:analysis*
chemical_list: D004731:Endotoxins; D013925:Thromboplastin