Kidney problem

Hi,

My cat black kitty recently stopped eating completely. I brought her to
the hospital after 2 days of not eating at all. The vet said she's has
swollen kidneys and extremely low body temperature at 98 degrees
(normal between 100 - 102?), and had to be admitted to the hospital
right away. She was put in ICU and given IV fluids and antibiotics.
We're be trying to get a proper diagnosis since then. She's been in the
hospital for 4 days(out of ICU now), but so far, they don't really know
what's wrong with her kidneys. They have done ultrasound, xrays and
blood work. Her urea nitrogen levels are very high (153) and her
creatinine levels are high(9.6) too. But we know she has no tumors in
her kidneys. She's only 6 or 7 (we don't know for sure cause she was a
stray), she's really too young to experience problems that old cats
would have. We are some what frustrated with our vet hospital because
they haven't really been able to give a definite diagnosis for us. They
tell us we need more testing. Our vet told us it might be cancer, or it
may be toxins that's causing this. To find out, they want to do a
biopsy on the kidneys. I have reservations about this as I've read in
other places where cats have died from this procedure. Also, performing
a biopsy might cause additional kidney damage to my kitty. Any one with
experience in this area? Or what we should do? Is a biopsy really
necessary for a diagnosis? Part of me wants to just keep her on
antibiotics and see how she does in a few weeks because they seem to
have helped in the last few days, but part of me is worried that her
condition will deterioate in the mean time.

We are on Long Island in the New York area. The vet's hospital is
Central Veterinary Associates in Valley Stream. If anyone has
information on their reputation or have gone through something similar
with this hospital, please share. I'm not 100% thrilled with them at
the moment, but am afraid to change because my cat is still very weak.

Thanks,
Kit