title: Transiently increased variation between a Point-of-Care and laboratory INR method after a long period of correlation: a case study demonstrating the need for ongoing correlation of POC with the central laboratory.
abstract: OBJECTIVE
  To perform long-term comparison between laboratory Stago and Point-of-Care (POC) i-STAT methods for determining the international normalized ratio (INR).
  
  
  METHODS
  This was a multicenter method comparison of patient INR results and factors related to performance variance.
  
  
  RESULTS
  For 5 years, the assays demonstrated close patient correlation within and above the 3.5 INR therapeutic range cutoff (bias, 0.23 INR units). Patient results above 3.5 INR were bimodal, with 60% demonstrating an i-STAT INR bias of less than 0.5. Several patient conditions were associated with the presence of a higher i-STAT bias. In year 6, a broader range i-STAT bias developed, increasing to 0.73 INR units. The increased bias persisted for 3 years, then returned to initial levels following i-STAT adjustments. The substantial increase in i-STAT bias after a long period of stability was partly corrected by renewed correlation to the international reference preparation. Additional assay drift is discussed in relation to thromboplastin reagents and other testing variables.
  
  
  CONCLUSIONS
  This study emphasizes the need for continual laboratory correlation with POC devices and caution in using published comparisons.
authors.affiliation: Dept of Pathology and Laboratory Medicine (113), VA Tennessee Valley Healthcare System, 1310 24th Ave S, Nashville, TN 37212-2637; gregory.sephel@va.gov.
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Sephel
authors.forename: Michael
authors.initials: M
authors.lastname: Laposata
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000097:blood; D001780:Blood Coagulation Tests / Q000379:methods / Q000592:standards / Q000706:statistics & numerical data*; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods / Q000706:statistics & numerical data*; D007755:Laboratories, Hospital / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D019095:Point-of-Care Systems / Q000592:standards / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D000925:Anticoagulants
keywords: Coagulation; Correlation; INR; Thromboplastin