I know A LOT about sport supplements and would be happy to answer any concerns you may have as best I can. I am not really up to speed on what comes out in your urine as I have had no need to know about that, but I can still give you a knowledgable push in the right direction.
It is difficult for me to tell you anything without knowing what you supplement your diet with, so for now I will give you some general advice -dont stop taking the supplements immediately before the medical if that is what you were going to do, this can cause all sorts of weird rebound type effects which can take a few days to even out and may possibly cause some concern.
I am not sure what is tested for in the medical, but I know sports supplements such as 'alcar' and 'choline' have been said to produce fats in the urine (on a good sport supplement forum I use) which may raise an eyebrow.