Verification of ISI in local laboratory

Prothrombine Time (PT) reagent is made of tissue factor buffered in calcium chloride. The sensitivity of different manufacturer’s reagents differs from each other. Sensitivity means how long PT is prolonged with deficiency of vitamin K dependent factors، especially factor VII. There are two kinds of ISI in each PT reagent kit: 1) Generic ISI 2) instrument and reagent specific ISI. Which one is used for INR calculation in your laboratory? Is it suitable for your instrument or needs local verification according to your facilities? Do you know that it is mandatory to verify ISI locally?