Expert: Jessica - 11/3/2010

Question
Dear Jessica
My 13yo Siamese cat, Fawn, recently had a blood and urine test (prior to GA for a dental) and they showed higher than normal urea (BUN?) levels. Vet diagnosed likely loss of kidney function (<66%) and so i am worried about chronic renal failure. (Vet gave him fluids and different painkillers/anaesthetic for the dental to reduce the stress of the GA on his kidneys and he came through it no problem.)
Fawn has shown no obvious symptoms of CRF, he's in good health (especially now the rotten teeth have been removed!) he is a nice bulky weight and has a great appetite. However he is very fussy about which foods he will eat.
I am looking into a low phosphorous kidney diet for him but have heard they are not palatable to a fussy cat. I have recently heard about Renalzin, which I believe is a paste that contains phosphorous binders, which stop the phosphorous being absorbed and so helps reduce damage to the kidneys.
Have you heard or had any experience with Renalzin? Is this a possible alternative to a prescription food? i would be grateful for any opinions or other advice you can offer.
Thanks so much for your time.
Becky

Answer
Hi Becky,

Renalzin is not yet available in the United States, so I don't have any experience with this phosphate binder in particular.  The active ingredient in Renalzin, lanthanum carbonate, is not commonly used as a phosphate binder in cats here, as the drug has only recently been approved for use at all.  However, other carbonates are commonly used and work in a similar fashion, and I have used them with my kidney patients.

I like the idea of them.  In my opinion, it's not worth making the kitty miserable for the remainder of his life, trying to force him to eat a food he doesn't enjoy.  And THE most important part of keeping a kidney patient healthy is to ensure that he eats.  Even if you have to feed him pure protein (which inherently contains high levels of phosphorus), then so be it.  And try to off-set it with a phosphate binder (the Renalzin sounds as good to me as any).

As for his blood urea nitrogen, I think it's wise to monitor his levels and limit his phosphorus, as kidney disease is so prevalent.  But creatinine levels are a stronger indication of kidney problems in cats than BUN levels are, and there can be other reasons besides kidney problems for an elevated BUN in the absence of elevated creatinine levels.  For instance, bleeding in the oral cavity or gastrointestinal tract can cause an elevation in BUN without an increase in creatinine.  Potentially, with his oral disease addressed, you might see an improvement in his BUN levels.  

I see that your vet ran some urine tests - did his urine come back within normal concentration ranges (specific gravity)?  Ideally, this is around 1.040 in a cat (normal reference is 10.015-1.060), and if he was within the normal range, then perhaps some of his elevated BUN might be explained by bleeding gums.  Just some extra information I have learned through experience.  If his urinary concentration is still normal, you may want to recheck his BUN after his gums have healed up.  If it has returned to normal, this could indicate good news.

Best of luck!

Jessica