Kitty has blood in urine, trying to figure out if anyone has had this before

Just gonna start off by saying already working with my vet, so far all we've been able to do is eliminate various things. More tests to come this month. Just curious if anyone has had anything like this before. I'm sure someone must have.

Sara has had blood in her urine pretty much every vet visit she's had since December (when she had a UTI). The blood then was not too unexpected, although it seemed like a bit more than would normally be expected. Last week, she had a lot of blood in her urine again (which has also been very dilute each time). There is no obvious UTI going on. X-ray eliminated bladder stone theory. She's on an antibiotic right now for infected tooth and abscessed anal gland. Have to go back to have her T4 rechecked (she has hyperthyroidism that got a bit out of control again) as well as blood pressure checked. Will check the urine again and assuming there will be blood again, will likely be doing a culture.

The main reason we didn't do a culture in July (when there was no UTI this time around) was because there was nothing bothering her. There still isn't, actually. But with all the problems she's been having (hyper-t, early CKD), I really don't want to chance it. I had a long chat with my vet last Friday, we talked about all the possibilities, and decided a culture would be the best route to go. If there is some long-term infection showing, they can treat it. Other things that it could be, there wouldn't be much we could do that wouldn't go into massive amounts of $$$ (talking thousands). Not to mention it would not likely add to the quality of her life to do these other procedures (if it did end up being any of the various things mentioned at the time). 

Has anyone had a cat that presented blood in the urine, without any other obvious problems that are related to that? She does seem like she has very early stage kidney disease. She had really bad hyperthyroidism when diagnosed, so I was told there was a good possibility she had it already (so not shocked). 

And she is 13, almost 14. 6lbs 1oz. 

Her WBC/RBC were slightly low back in July, but they were normal (don't have the numbers in front of me unfortunately) last week. 

There is a condition called idiopathic cystitis which affects some kitties.  http://www.petmd.com/blogs/fullyvetted/2011/dec/treating_feline_idiopathic_cystitis-12092   You can also google feline idiopathic cystitis and get numerous articles about it.  The prevailing theory is that it is stress related but that isn't conclusive.  You can start with the easy things like running feliway diffusers and see if that helps.  Some kitties have such a severe case that they are given a tranquilizer called amitriptyline  which eases bladder spasms.  I remember when I was in the service many many years ago all soldiers in combat carried two pre-filled syringes of that as first aid for nerve gas exposure.  I am sure that it is a much smaller dose.

I would ask your vet about the possibility of this being the issue.

Is that anything like interstitial cystitis in humans? I remember that being something they typically diagnosed based on symptoms alone, diagnosing via tests is not impossible, but typically not done as it requires anesthetic. And I'm sure my vet mentioned that as a possibility - just so many things were mentioned my tiny little brain was overwhelmed.

She has always seemed stressed out the entire time I've had her. I got her at 4 years old and suspect she was abused. She used to pull her hair out. She stopped doing that after a few years. She also always seems on edge. That tail is CONSTANTLY twitching. You know how cats are when they are agitated? Yeah, that's her. All the time. That IS her normal.