My sisters dog urinated inside tonight and the urine has blood in it. Any idea what could be going on?

I stepped in it. He has never urinated inside the house before so this is disturbing. Any idea what could be going on. She is on the phone right now trying to get him to a vet. But it looks like she might have to wait a few days before they will see the dog. And should we collect a sample of the bloody urine or mop it up?