You don't have to wait until the next poo to take the snake in to see the vet. It could be weeks before you see another one. The vet can usually get a sample "the hard way" if they need one. With signs of blood, I wouldn't wait.

The one thing that came to mind though...did the snake shed about the same time the poo was laid? Because shedding sometimes can cause bleeding around the vent and that is perfectly normal and heals up very quickly.