The value assigned to a batch of thromboplastin reagent by reference to a ‘working reference’ reagent which has been calibrated against internationally accepted standard reference preparations with an ISI value of 1. The more sensitive the thromboplastin reagent, the longer the resulting prothrombin time (PT); its ISI will be less than 1. The ISI value allows comparison of coagulation times estimated in different laboratories. See international normalized ratio.
Subjects: Medicine and Health.