Which laboratory test is used to monitor oral anticoagulant (warfarin) therapy?

Question

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The PT (prothrombin time) is used to monitor oral anticoagulant therapy with warfarin. It measures the activity of several clotting factors, including factor II, which is affected by warfarin. The goal of warfarin therapy is to achieve a target INR (international normalized ratio) within a therapeutic range, which is usually 2.0-3.0. A high INR indicates increased risk of bleeding, while a low INR indicates increased risk of clotting. APTT (activated partial thromboplastin time) is used to monitor heparin therapy, TT (thrombin time) measures the time it takes for fibrin clot formation in the absence of platelets, and fibrinogen levels reflect fibrinogen production, consumption or degradation, but neither of these tests are used to monitor warfarin therapy.

Which Laboratory Test Is Used to Monitor Oral Anticoagulant (Warfarin)