title: Point-of-care monitoring of vitamin K-antagonists: validation of CoaguChek XS test strips with International Standard thromboplastin.
abstract: OBJECTIVE
  Many patients treated with vitamin K-antagonists (VKA) use point-of-care (POC) whole blood coagulometers for self-testing. The majority of patients in the Netherlands use one type of POC coagulometer, that is, the CoaguChek XS. Each new lot of test strips for the CoaguChek XS is validated by a group of collaborating thrombosis centres. We assessed the International Normalised Ratio (INR) differences between each of 51 new lots of test strips and the International Standard for thromboplastin rTF/95 or its successor rTF/09.
  
  
  METHODS
  Each year, a particular lot of CoaguChek XS test strips was used as reference lot. The reference lot was validated by comparison to the International Standard, yielding a relationship between the reference lot INR and International Standard INR. Successive lots of test strips were compared to the reference lot by three centres using 19-29 capillary blood samples obtained from VKA-treated patients. Each patient provided two blood drops from the same finger prick, one for the reference lot strip and one for the new lot.
  
  
  RESULTS
  The mean INR differences between each lot and the International Standard varied between -8% and +4%. The mean absolute values of the relative differences varied between 2.4% and 8.1%. There were small but clinically unimportant differences in INR between the first and second drop of blood.
  
  
  CONCLUSIONS
  Accuracy of CoaguChek XS INR determinations can be assessed by a group of collaborating centres using a limited number of capillary blood samples. As the mean INR differences with the International Standard were smaller than 10%, the lots were approved for use by the Netherlands Thrombosis Services.
authors.affiliation: Department of Thrombosis and Hemostasis, Leiden University Medical Centre, Leiden, The Netherlands. a.m.h.p.van_den_besselaar@lumc.nl
authors.forename: Anton M H P
authors.initials: AM
authors.lastname: van den Besselaar
authors.forename: Nathalie C V
authors.initials: NC
authors.lastname: Péquériaux
authors.forename: Marij
authors.initials: M
authors.lastname: Ebben
authors.forename: Joke
authors.initials: J
authors.lastname: van der Feest
authors.forename: Kerst
authors.initials: K
authors.lastname: de Jong
authors.forename: Maria B J
authors.initials: MB
authors.lastname: Ganzeboom
authors.forename: Jetty
authors.initials: J
authors.lastname: van Ooijen
authors.forename: Ferna
authors.initials: F
authors.lastname: Postema
authors.forename: Evelina
authors.initials: E
authors.lastname: Witteveen
authors.forename: Felix J M
authors.initials: FJ
authors.lastname: van der Meer
mesh_terms: D000925:Anticoagulants / Q000627:therapeutic use*; D001777:Blood Coagulation; D016903:Drug Monitoring / Q000379:methods* / Q000592:standards; D006403:Hematologic Tests; D006801:Humans; D019934:International Normalized Ratio; D019095:Point-of-Care Systems / Q000592:standards; D011933:Reagent Kits, Diagnostic; D013925:Thromboplastin / Q000032:analysis* / Q000592:standards; D014812:Vitamin K / Q000037:antagonists & inhibitors*
chemical_list: D000925:Anticoagulants; D011933:Reagent Kits, Diagnostic; D014812:Vitamin K; D013925:Thromboplastin