Most of the time, signs of blood are a good reason to get to the vet soon. But if the blood IS coming from the feet just from cracks due to the wheel, that's usually not a big deal. Feet tend to heal quickly and often it can even be hard to find the cracks or cuts the morning after. Taking the wheel out for a night can help rest them, but can also cause the hedgehog to climb the cage, so you have to be careful.
Wheels with ribs can be more likely to cause bloody feet, but even smooth wheels can cause it if the hedgehog isn't used to running and has tender feet. Usually the feet toughen up after once or twice & there are no more issues, but it's a good idea to keep a close eye on them, and if they continue to end up with bloody feet, then it might not be a bad idea to check in with a vet. And of course, if there are any other unusual things (like the feet swelling up, looking red/sore, change in activity, etc.), then see the vet.
~*~*~ Kelsey ~*~*~
RIP my sweet Lily ~ 6/12/08 - 1/20/12