Spayed cat going into heat?

Question
I had a feral cat living under my porch, Last June she was laying on my front porch couldn't move and looked very sick. My local Spca wouldn't help me, so I took her to my vet, She had to have a full hysterectomy because she had 2 dead kittens in her! So six months after all of this she goes into heat! Took her to the vet she had blood in her urine, no temp, or any other signs of infection. So he puts her on an antibiotic, and the heat symptoms go away, the blood in her urine is gone also! So 1 week after being off the antibiotic, she goes back into heat. This has been pretty much 4 straight months of her being in heat, and me and my vet are stumped! Can you help me?

Answer
Hi Melissa.  Well something strange is going on!

The issues of blood in her urine and being in heat are separate.  Unlike dogs, cats don't bleed during heat, so if there is blood in her urine, it's being caused by an infection, urinary tract crystals, or an inflammatory condition known as interstitial cystitis.  That shouldn't cause heat symptoms, but it can cause frequent urination, inappropriate urination, vocalization during urination, and excessive licking around the genital area.  Might these have been confused for signs of estrus?  Antibiotics would help abate these symptoms if the problem was an infection, but it shouldn't have any effect on her heat.

As for the heat, if she is clearly going into estrus, I think your vet needs to consider the possibility of an incomplete spay.  What stops cats from going into heat after they are spayed is the complete removal of the ovaries.  More commonly that you may think, some ovarian tissue is left behind during the procedure.  Just a tiny piece of missed ovarian tissue produces enough hormones to cause the cat to have regular heat cycles (this is called Ovarian Remnant Syndrome).  It's strange that she'd have a heat that lasted 4 entire months, but I can't think of any other explanation.  Your vet can take blood tests that can confirm whether hormone levels are consistent with an incomplete spay.  Or, he can do an exploratory surgery to search for and remove the missed ovarian tissue.

Great work getting this kitty in to your own vet when no one else would help her out.  I wish there were more folks like you!

Best of luck!

Jessica