Blood in your dogs urine can be caused by something less serious and then it can also mean something more serious is going on.
Dogs can have blood in their urine for a variety of reasons.
Some reasons that your dog may have blood in their urine is due to Urinary tract infections, bladder or kidney stones, cancer and systemic bleeding disorders.
If your dog continues to experience blood in the urine for more than a few days then it would be a good idea to take the dog to the vet to have the dog checked out.
Sometimes it's just a Urinary Tract Infection that goes away on it's own within a few weeks or so but if it's something more serious then a vet needs to treat the dog for the condition.