Recommended method for reporting prothrombin time results to control oral anticoagulation.
Utilized to regulate the dosage of warfarin by aiming for a target INR result.
A mathematical conversion of a patient’s PT that accounts for the sensitivity of the thromboplastin used in a given laboratory by factoring in the international sensitivity index value supplied by the manufacturer.
Calculated by the patient PT/ the geometric mean of the PT of at least 20 healthy subjects of both sexes tested at the performing laboratory.
Only half of the patients on oral anticoagulants are within the target INR at any given time.
Over the INR range of 1.3-1.9 the mean factor levels of FII ranges from 31-65%, FV from 40-70% FVII from 22-60%(Dietcher).
International normalized ratio (INR)-
Indication Target INR
Pulmonary embolism 2.5
Deep vein thromboembolism 2.5
Recurrent venous thromboembolism 2.5
off anticoagulants
Recurrent venous thromboembolism 3.5
on warfarin
Symptomatic inherited thrombophilia 2.5
Antiphospholipid syndrome 3.5
Atrial fibrillation 2.5
Cardioversion 2.5
Mural thrombosis 2.5
Cardiomyopathy 2.5
Mechanical valve 3.5