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      Standardization of Prothrombin Time/International Normalized Ratio (PT/INR).

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          Abstract

          The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT 'correction factors', namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a 'general' or 'generic' ISI and others being reagent/coagulometer-specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.

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          Author and article information

          Journal
          Int J Lab Hematol
          International journal of laboratory hematology
          Wiley
          1751-553X
          1751-5521
          Feb 2021
          : 43
          : 1
          Affiliations
          [1 ] Department of Hematology and Blood Transfusion, School of Allied Medicine, Iran University of Medical Sciences, Tehran, Iran.
          [2 ] Department of Haematology, Sydney Centres for Thrombosis and Haemostasis, Institute of Clinical Pathology and Medical Research, NSW Health Pathology, Westmead Hospital, Westmead, NSW, Australia.
          [3 ] Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran.
          [4 ] Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran.
          Article
          10.1111/ijlh.13349
          32979036
          fb372515-58b3-47cf-86f8-e36eb8c6e5bd
          History

          INR,coagulation factors,harmonization,hemostasis,prothrombin time,standardization

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