title: Accuracy and precision of the CoaguChek S versus laboratory INRs in a clinic.
abstract: BACKGROUND
  The CoaguChek S is the next-generation coagulation monitor for measuring the international normalized ratio (INR) that replaces the CoaguChek device. Studies are lacking comparing the CoaguChek S with local laboratory INR assessment to ensure its accuracy and precision for monitoring patients on anticoagulation.
  
  
  OBJECTIVE
  To evaluate accuracy, precision, and technical ease-of-use of the CoaguChek S compared with laboratory measurements.
  
  
  METHODS
  Accuracy was evaluated in 101 patients by parallel assessment of INRs (CoaguChek S and laboratory); precision was evaluated in 31 patients using duplicate INRs from CoaguChek S and laboratory and from liquid quality controls. Accuracy was determined using orthogonal regression, Bland-Altman plot, and clinical applicability (INRs discrepant in categorization of INR goal and resulting in different therapeutic decisions). Precision was examined by comparing mean difference +/- SD between repeated INRs from CoaguChek S and laboratory, coefficient of variation (CV), and coefficient of repeatability (CR). The influence of low and elevated INRs on accuracy and precision was also examined. To assess ease-of-use of the monitor, the number of technical errors was recorded.
  
  
  RESULTS
  The CoaguChek S significantly correlated to laboratory measurement (r = 0.93); 16.7% of INRs resulted in discrepant categorization and 24.5% would have required a different therapeutic plan. The CV and CR compared well between CoaguChek S and laboratory (6% vs. 4.9%; 0.455 vs. 0.346, respectively). When subgroups of INR values <4.0 and <3.0 were evaluated, the precision improved with both methods. Precision, based on liquid quality controls, was good (CV 4.6% = low-level; 3.3% = high-level). The CoaguChek S was found to have an error rate of 1.8%.
  
  
  CONCLUSIONS
  The CoaguChek S is an accurate and precise alternative to laboratory assessment of the INR at values <4.0; it is an efficient device with a low likelihood of errors during testing.
authors.affiliation: College of Pharmacy, University of Oklahoma Health Sciences Center, 1110 N. Stonewall, Oklahoma City, OK 73190-5040, USA. Dawn-Havrda@ouhsc.edu
authors.forename: Dawn E
authors.initials: DE
authors.lastname: Havrda
authors.forename: Toni L
authors.initials: TL
authors.lastname: Hawk
authors.forename: Carrie M
authors.initials: CM
authors.lastname: Marvin
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology / Q000627:therapeutic use; D001777:Blood Coagulation / Q000187:drug effects; D001780:Blood Coagulation Tests / Q000379:methods / Q000592:standards*; D005260:Female; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods / Q000592:standards*; D008297:Male; D008875:Middle Aged; D011517:Prothrombin Time; D015203:Reproducibility of Results; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D014859:Warfarin