Kidney Disease vs. Chronic Pyelonephritis

Recently my 18.5 yr. old cat started urinating outside her box and going more frequently, sleeping excessively, difficulty getting around (back leg weakness), and vomited with diarrhea say before took her to Vet.  After bloodwork to check kidney function, Vet started her on antibiotic to treat her for suspected Chronic Pyelonephritis, to continue for 6 weeks.  She had a fever over 106 on day of exam.  She is responding well to antibiotic, hind end weakness improved somewhat.  However, she is eating far less, and continues to lose weight (< 7.5 lbs.).  Uses litter box, but still urinating frequently and drinks fair amount of water.  Is there a way to tell if she has kidney disease/failure and not pyelonephritis without doing an ultrasound?

[Dr. Carol Osborne, DVM]

Hello, If it is possible to post your cats blood and urine results it would help us to help you. Yes its possible to differentiate between kidney disease and pyelonephritis and depending on your lab values for blood and urine there are a couple other tests that may also be useful. You mentioned weight loss and a hyperactive thyroid. This is quite common in teen aged cats and may be the underlying cause of many of these issues. You might have your vet check that the blood levels of the medication she is taking for her hyperactive thyroid are appropriate to keep her thyroid levels in the normal range. When you see her losing weight and having diarrhea that is often a sign that the thyroid medication dosage is too low as the signs of over or hyperactive thyroids are recurring.  There are many issues that your cat may be experiencing which all may or may not be related. Her kidney failure may be responsible for the vomiting and appetite loss and fluids are very helpful to flush and eliminate toxins from her body in lieu of the fact that with kidney failure toxins normally eliminated by the kidneys can build up within the body. I would be sure a urinalysis was run with a specific gravity to further evaluate her kidney function and help rule out for example a urinary tract infection which can cause excessive urination which then leads to dehydration and complicates the failing kidneys further. Be sure to verify with your vet that her heart function is normal. Were x-rays taken? Since this is a fairly complex case, there are Board Certified Veterinary Internists that have received additional years of formal education in internal medicine and specialize in cases like this. A board certified veterinary internist may prove to be quite helpful for your cat if you are considering a second opinion.
Thank you
Dr Carol Osborne, DVM

[Mybones]

This is followup to Dr. Osborne's reply.  I was able to obtain the blood and urine values, they are as follows:
BUN                             70
Creatinin                       2.4
WBC                            248
  Neutrophils                  78%

Urinalysis                       > 30 white cells for high power field

I am presently trying to find a board certified internist.  The first one I contacted isn't accepting new patients.  No x-rays were taken.  The blood levels of her Thyroid medication was fine according to my Vet.

Thank you.