Monitoring Oral Anticoagulant Therapy with Vitamin K Antagonists

Research output: Chapter in Book/Report/Conference proceedingChapter


Coumarin drugs are widely used to treat and prevent venous thromboembolism, to prevent stroke and systemic embolism in atrial fibrillation and in patients with prosthetic heart valves. Due to its relatively narrow therapeutic window, interaction with diet and other drugs, this treatment requires frequent dose-adjustment by means of laboratory testing. The test of choice is the prothrombin time (PT), because the large between-thromboplastin results variability needs to be standardized. The international normalized ratio (INR) is the current system of standardization endorsed by the World Health Organization (WHO). This chapter is aimed at discussing the principle of this system of standardization with particular emphasis to the thromboplastin calibration, including the WHO model and the establishment and hierarchy of international standards for thromboplastins; the local calibration; how the PT is converted into INR and the issue that may affect results; the validity limitations of the INR and the its implementation. This edition first published 2013

Original languageEnglish
Title of host publicationQuality in Laboratory Hemostasis and Thrombosis, Second Edition
PublisherJohn Wiley and Sons
Number of pages11
ISBN (Print)9780470671191
Publication statusPublished - Feb 26 2013


  • 67 40
  • CRM 149 S
  • International normalized ratio
  • Local calibration
  • Prothrombin time
  • RBT 05
  • RTF 09
  • RTF 95
  • Thromboplastin
  • Vitamin K antagonists

ASJC Scopus subject areas

  • Medicine(all)


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