Even Healthy Cats Act Sick When Their Routine Is Disrupted
I always felt that one of cat's interstitial cystitis boughs are brought on by stress. It never fails. A few days after we go away for a weekend she starts peeing outside the box and it progresses to blood in the urine if we don't get a handle on it quick enough. And yes I do take her to the vet and it is not a bacterial infection.
Here is a link that might be useful: Article