title: Warfarin does not interfere with lupus anticoagulant detection by dilute Russell's viper venom time.
abstract: BACKGROUND
  The dilute Russell's viper venom time (DRVVT) test is part of the diagnostic armamentarium used to detect lupus anticoagulant (LA). When testing patients on warfarin therapy, there is some concern of false positive results due to their low Factor X levels. We studied the diagnostic performance of the DRVVT ratio (DRVVT-R) to confirm the presence of LA in thrombophilia patients receiving warfarin therapy, and compared those results with a control group receiving warfarin for cardiac conditions but without thrombosis.
  
  
  METHODS
  The DRVVT (screen, confirm, and ratio), Factors II and X assays, and PT/INR were performed in patients receiving warfarin for thrombosis and in patients with cardiac conditions but no thrombosis (control group).
  
  
  RESULTS
  Patients on warfarin in the thrombosis group (n=22) were positive for LA by DRVVT-R (ratio >1.27 was considered positive) whereas none of the patients in the control group (n=13) were positive for LA. The median DRVVT-R was significantly higher in the thrombosis group (1.60, range 1.29-1.92) as compared to controls (1.13, range 0.79-1.23, p<0.001) even though the INRs were comparable (median 2.3 for thrombosis group versus median of 2.2 for controls, p<0.05). Similarly, FX and FII levels were not significantly different in these two groups.
  
  
  CONCLUSIONS
  We conclude that the use of the DRVVT-R allows for diagnosis of LA in patients receiving warfarin with therapeutic INR despite their decreased Factor X levels.
authors.affiliation: Department of Pathology, University Hospitals of Cleveland, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Horatiu
authors.initials: H
authors.lastname: Olteanu
authors.forename: Katharine A
authors.initials: KA
authors.lastname: Downes
authors.forename: Jigar
authors.initials: J
authors.lastname: Patel
authors.forename: Darja
authors.initials: D
authors.lastname: Praprotnik
authors.forename: Ravindra
authors.initials: R
authors.lastname: Sarode
mesh_terms: D000368:Aged; D001777:Blood Coagulation / Q000187:drug effects; D003627:Data Interpretation, Statistical; D005170:Factor X / Q000032:analysis; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D016682:Lupus Coagulation Inhibitor / Q000097:blood*; D008297:Male; D011516:Prothrombin / Q000032:analysis; D011517:Prothrombin Time; D019851:Thrombophilia / Q000378:metabolism; D013927:Thrombosis / Q000188:drug therapy; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D016682:Lupus Coagulation Inhibitor; D014859:Warfarin; D011516:Prothrombin; D005170:Factor X