title: Analytical accuracy and precision of two novel Point-of-Care systems for INR determination.
abstract: BACKGROUND
  Portable point-of-care (POC) instruments for determination of the whole blood prothrombin time (PT) have been available for the last three decades. Recently, two novel POC instruments for PT and International Normalized Ratio (INR) determination in whole blood have been manufactured. The purpose of this study was to compare INR values obtained with the novel instruments (microINR® and ProTime InRhythm™) to the INR determined with the international standard for thromboplastin rTF/09.
  
  
  METHODS
  In 60 patients treated with vitamin K-antagonists, venous whole blood was analysed with four different types of POC instruments including the novel ones. In the same patients, citrated plasma was analysed with the international standard rTF/09 and the manual tilt tube technique for clotting time determination. We assessed the bias of the INR read from the POC instruments relative to the international standard. To study the imprecision of the two novel POC instruments, duplicate INR determinations were performed.
  
  
  RESULTS
  The results obtained with the two novel POC instruments were positively correlated with those of the international standard rTF/09. However, there was a significant bias between INR read from the novel instruments and the INR determined with rTF/09 (P < 0.001). The mean bias was -13.7% (MicroINR) and -9.3% (InRhythm). The imprecision coefficient of variation in venous blood was 5.0% and 5.1%, respectively.
  
  
  CONCLUSIONS
  The imprecision of the two novel instruments is acceptable with respect to the average within-subject variation of the INR. The accuracy of the systems is borderline and should be improved by the manufacturers.
authors.affiliation: Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: a.m.h.p.van_den_besselaar@lumc.nl.
authors.forename: A M H P
authors.initials: AM
authors.lastname: van den Besselaar
authors.affiliation: Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: F J M
authors.initials: FJ
authors.lastname: van der Meer
authors.affiliation: Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: C F
authors.initials: CF
authors.lastname: Abdoel
authors.affiliation: Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Witteveen
mesh_terms: D002138:Calibration; D005260:Female; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods*; D008297:Male; D019095:Point-of-Care Systems; D011517:Prothrombin Time