I had a real problem with this after my longer runs last year. I went to the Dr. who sent me to get a colonoscopy. Everything checked out fine. Nothing was wrong with me.

If insurance can cover it, I say go get it done for piece of mind.

I took an article to the Dr. (the one who did the colonoscopy) about endurance athletes having this issue, and he shrugged it off. Wouldn't even consider the idea. Personally I think he hasn't ever seen an endurance athlete and doesn't understand how the body of an ahlete functions.

Obviously better safe than sorry... so getting the tests run will let you know nothing is wrong.