This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Which of the following is done for a patient on coumarin (warfarin) therapy: \nSelect and explain. \nA. Partial thromboplastin time (PTT), B. Prothrombin time (PT), C. Bleeding time (BT), D. Capillary fragility test (CFT)', 'role': 'user'}, {'content': 'Answer: B \nExplanation: When a coumarin, such as warfarin, is given to a patient, the amounts of active prothrombin and Factors VII, IX, and\xa0X,\xa0all\xa0 formed\xa0by\xa0the\xa0liver,\xa0begin\xa0to\xa0fall.\xa0\nProthrombin time gives an indication of the concentra\xadtion of prothrombin in the blood.\nThe normal prothrombin time is about 12 seconds.\nReference:\xa0 Ganong Physiology 25th ed page no 492,493', 'role': 'assistant'}]