Why don't you tell them about the garlic but just fudge a little on the date you stopped taking it. That way they will be sure to test your blood, which I would think they'd do anyway. I have heard that Vitamin K as found in collards and other greens can thicken the blood. Maybe a meal of those would be all you'd need. Sorry I'm not an expert but it seems to me you need answers and really the truth is always the best way to go. But I understand you really want this surgery.