title: Effect of coagulation factors on discrepancies in International Normalized Ratio results between instruments.
abstract: BACKGROUND
  The reasons for discrepancies between International Normalized Ratio (INR) results determined by point-of-care-instruments and laboratory measurements are not fully understood. In this study we investigated whether different levels of coagulation factors in the plasma of patients can explain some of the systematic and/or random parts of the difference in INR between the instruments.
  
  
  METHODS
  Blood samples were collected at four different patient visits from each of 34 outpatients on warfarin treatment. INR was determined on a laboratory instrument (STA Compact(®)) and on three point-of-care instruments (Simple Simon(®)PT, CoaguChek(®)XS and INRatio™). In addition, the level of fibrinogen, coagulation factors II, V, VII and X was determined. INR instruments were compared in pairs. Simple linear regressions as well as multiple linear regressions and nested ANOVA analyses were used to examine the data.
  
  
  RESULTS
  The coagulation factors, especially fibrinogen, factors II and VII, could explain between 16% and 45% of the total variance of the differences in INR between instruments dependent on instruments compared. After correction for factors no systematic difference was seen for four of the six comparisons and the between- and within-subject variation of the differences were reduced by up to 69% and 52%, respectively.
  
  
  CONCLUSIONS
  By correcting for the appropriate coagulation factors, especially the systematic differences, but also the between- and within-subject variation of the differences between instruments, were reduced. This indicates that different levels of coagulation factors in the plasma of the patients play an important role in explaining discrepancies between INR instruments.
authors.affiliation: Department of Public Health and Primary Health Care, Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway. una.solvik@isf.uib.no
authors.forename: Una Ørvim
authors.initials: UØ
authors.lastname: Sølvik
authors.forename: Thomas Helge
authors.initials: TH
authors.lastname: Røraas
authors.forename: Per Hyltoft
authors.initials: PH
authors.lastname: Petersen
authors.forename: Anne Vegard
authors.initials: AV
authors.lastname: Stavelin
authors.forename: Grete
authors.initials: G
authors.lastname: Monsen
authors.forename: Sverre
authors.initials: S
authors.lastname: Sandberg
mesh_terms: D000704:Analysis of Variance; D000925:Anticoagulants / Q000737:chemistry / Q000627:therapeutic use; D001779:Blood Coagulation Factors / Q000032:analysis*; D006801:Humans; D019934:International Normalized Ratio / Q000295:instrumentation*; D007755:Laboratories, Hospital; D016014:Linear Models; D019095:Point-of-Care Systems; D013927:Thrombosis / Q000188:drug therapy; D014859:Warfarin / Q000737:chemistry / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D001779:Blood Coagulation Factors; D014859:Warfarin