A standardized way of reporting prothrombin time results that accounts for differences between laboratories. Target INR ranges from 2.0-3.0 for most conditions requiring anticoagulation.
Introduced in 1983 by the World Health Organization to standardize warfarin monitoring globally. The word 'normalized' indicates adjustment to a common reference standard, eliminating lab-to-lab variation.
Before INR, the same blood sample could give wildly different results at different hospitals, making warfarin dosing dangerous! The INR solved this by mathematically converting all results to what they would be using a standard reference reagent - it's like having a universal translator for clotting tests.
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