Coagulation
Coagulation laboratory tests
International sensitivity index (ISI)



Topic Completed: 1 November 2012

Revised: 7 January 2019, last major update November 2012

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PubMed Search: International sensitivity index [title]


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Table of Contents
Definition / general
Cite this page: Parsons J. International sensitivity index (ISI). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/coagulationISI.html. Accessed December 8th, 2019.
Definition / general
  • Measure of sensitivity of particular PT reagent - determined by manufacturer
  • Used to resolve interlaboratory variations in PT (Arch Pathol Lab Med 2004;128:308, J Clin Pathol 2003;56:114)
  • Different PT reagents have different sensitivities to factor deficiencies
  • High ISI (3.0) means insensitive reagent vs. low ISI (1.0) means sensitive reagent
  • Labs should use reagents with an ISI of 1.0 to 1.5, if possible
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