I've never had experience with bloody urates before and the limited reading (only since you've posted this thread) seems to suggest there could be a problem that warrants a visit to the vet. One page stated that any blood in a snake's urate is bad and a bacteriological exam by your vet will need to be performed. Another person who posted on another site with a similar problem found his snake was suffering from amoebic dysentry. I find the latter unlikely as dysentry (IMO) would also mean your snake would have the runs.
Sorry for not being any help. I hope someone with experience in this matter can shed some more light on the problem. If anything, this will bump your post up. Good luck.