title: Contributions of procoagulants and anticoagulants to the international normalized ratio and thrombin generation assay in patients treated with warfarin: potential role of protein Z as a powerful determinant of coagulation assays.
abstract: BACKGROUND
  The effects of warfarin are measured with the international normalized ratio (INR). However, the thrombin generation assay (TGA) may offer more information about global coagulation. We analyzed the monitoring performance of the TGA and INR and investigated the impact of procoagulants (fibrinogen, factor (F)II, FVII, FIX, and FX) and anticoagulants (proteins C, S, and Z) on them.
  
  
  METHODS
  The TGA was performed on a calibrated automated thrombogram, producing lag time, endogenous thrombin potential (ETP), and peak thrombin in 239 patients treated with warfarin. Pro- and anticoagulant levels were also measured.
  
  
  RESULTS
  The INR was significantly and inversely correlated with ETP. The therapeutic range of ETP comparable to an INR range of 2.0-3.0 was 290.1-494.6. ETP showed comparable performance to the INR as a warfarin-monitoring parameter with respect to clinical complication rate. The median levels of FII, FVII, FIX, and FX and proteins C and Z tended to decrease gradually with increasing anticoagulation intensity according to the INR or ETP. Of note, protein Z levels decreased dramatically with increasing anticoagulation status. INRs were significantly determined by FII, FVII, and protein Z. ETP was significantly dependent on FVII, and proteins C and Z concentration. Protein Z significantly reduced the total amount of thrombin generation and prolonged PT value in vitro.
  
  
  CONCLUSIONS
  The INR and ETP exhibit similar efficacy for warfarin monitoring according to the clinical complication rate. Protein Z is considered to be a significant determinant of INR and ETP in patients on warfarin therapy.
authors.affiliation: Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Qute
authors.initials: Q
authors.lastname: Choi
authors.forename: Ji-Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Jungwon
authors.initials: J
authors.lastname: Hyun
authors.forename: Kyou-Sup
authors.initials: KS
authors.lastname: Han
authors.forename: Hyun Kyung
authors.initials: HK
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000627:therapeutic use*; D001779:Blood Coagulation Factors / Q000378:metabolism; D001780:Blood Coagulation Tests / Q000379:methods*; D001798:Blood Proteins / Q000378:metabolism*; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods; D008297:Male; D008875:Middle Aged; D011486:Protein C / Q000378:metabolism; D017293:Protein S / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism*; D014859:Warfarin / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D001779:Blood Coagulation Factors; D001798:Blood Proteins; D011486:Protein C; D017293:Protein S; C026080:plasma protein Z; D014859:Warfarin; D013917:Thrombin
keywords: ETP; F; INR; PT; TF; TGA; coagulation factor; endogenous thrombin potential; international normalized ratio; prothrombin time; thrombin generation assay; tissue factor