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European Concerted Action on Anticoagulation. A multicentre calibration study of WHO international reference preparations for thromboplastin, rabbit (RBT/90) and human (rTF/95)
  1. L Poller1,
  2. M Keown1,
  3. N Chauhan1,
  4. A M H P van den Besselaar2,
  5. A Tripodi3,
  6. C Shiach4,
  7. J Jespersen5
  1. 1ECAA Central Facility, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
  2. 2Haemostasis and Thrombosis Research Centre, Leiden University Medical Centre, 2300 RC Leiden, The Netherlands
  3. 3A Bianchi Bonomi, Haemophilia and Thrombosis Centre, IRCCS Maggiore Hospital, University of Milan, 20122 Milan, Italy
  4. 4Department of Haematology, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK
  5. 5Department for Thrombosis Research, University of Southern Denmark and Department of Clinical Biochemistry, Ribe County Hospital, Esbjerg, DK-6700 Denmark
  1. Correspondence to:
 Professor L Poller
 ECAA Central Facility, Faculty of Life Sciences, The University of Manchester, Manchester;


A 10 centre calibration was performed after six years to determine the international sensitivity index (ISI) of rTF/95 relative to RBT/90, and to assess any international normalised ratio (INR) bias compared with the original multicentre calibration. After exclusion of one outlying centre, the follow up calibration gave a mean ISI for rTF/95 of 0.99, which although a small difference, is significantly greater than the mean ISI of 0.94 obtained previously. The change in ISI for international reference preparation (IRP) rTF/95 relative to RBT/90 would lead to a slight bias in INR for human compared with rabbit thromboplastins. At a theoretical INR of 3.0, the INR bias is 6.0%, and this is below the accepted 10% level of clinical relevance. Ongoing stability monitoring of World Health Organisation thromboplastin IRP is advised.

  • CV, coefficient of variation
  • ECAA, European Concerted Action on Anticoagulation
  • INR, international normalised ratio
  • IRP, international reference preparation
  • ISI, international sensitivity index
  • PR, prothrombin ratio
  • PT, prothrombin time
  • WHO, World Health Organisation
  • international normalised ratio
  • international sensitivity index
  • multicentre calibration
  • international reference preparation

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  • The study was supported by EC Standards, Measurements and Testing Programme (grant number SMT4-CT98-2269) and an additional research grant from the Manchester Thrombosis Research Foundation. Gratitude is expressed to WHO Biologicals for the supply of RBT/90 and rTF/95 IRP.