Coagulation laboratory tests
International sensitivity index (ISI)

Author: Jeremy Parsons, M.D. (see Authors page)

Revised: 16 May 2016, last major update November 2012

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

PubMed Search: International sensitivity index [title]

Table of Contents
Definition / general
Cite this page: International sensitivity index (ISI). website. Accessed December 13th, 2018.
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