Coagulation laboratory tests
International sensitivity index (ISI)

Topic Completed: 1 November 2012

Revised: 7 January 2019, last major update November 2012

Copyright: (c) 2002-2016,, Inc.

PubMed Search: International sensitivity index [title]

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Definition / general
Cite this page: Parsons J. International sensitivity index (ISI). website. Accessed May 29th, 2020.
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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