Clot in left leg

My forty year old son recently had a blood clot in his left leg that ran the length of his leg up to his groin. He was on IV heparin and Coumadin, 10mg, and hospitalized for one-week. They were never able to get his INR to a therapeutic level, even at this high dose, discharging him at 1.7. He eventually got his INR to 2.3. He is still on Coumadin and his current dose was just increased to 12.5mg a day as his last INR was 1.2! Through all of this, he still has the blood clot in his calf and it is very swollen. He has constant pain if he is on his feet. He is a tall, athletic male who is not overweight, doesn't smoke, drinks in moderation, exercises, and eats healthy. He has not eaten any greens or foods that would affect his INR. He is going to see a hematologist next week. I would like him to go to Mayo to see a specialist but he trusts his doctor. Should I be concerned?