This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bleeding Disorders, Subject name: Pathology
[{'content': 'Warfarin therapy is monitored by: \nSelect and explain. \nA. PT INR, B. apTT, C. Vit K levels, D. PT', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. (a) PT INR(Ref: Wintrobe's 12th ed/pg 1489)Patients with recurrent thrombosis should receive longterm warfarin therapy at a dosage to maintain an international normalized ratio (INR) value of 2.0 to 3.0.", 'role': 'assistant'}]