Dear Siouxsie and Thomas:
My 17-year-old cat, Mr. Louie, has been diagnosed with kidney failure. My vet told me the test, which was called a "profile pre-anesthetic" test that tests for 6 common problems including liver, glucose, T-Pro, and kidney (BUN 33 and Cre 2.5) -- the only concern was the Cre was 2.5 and normal is 2.0 mg/dl. She told me that it wasn't a large increase (.5 mg/dl), but to start potassium twice a day and special formulated food for kidney failing cats, only sold by vets.

The original reason we went to the vet was a bad tooth. He will go in Monday to have the tooth pulled and the rest of the teeth cleaned. He's been on an antibiotic and the vet says he will continue antibiotics for several weeks.

Okay, enough history. My questions are -- in your opinion, of course: 1. Are blood tests compromised easily and do the results vary quite a bit? 2. What does a .5 mg/dl increase tell you? 3. With just a .5 mg/dl increase in the Cre test, does that still mean the kidneys are 60-70% gone already?

Thank you for your opinion, I will continue to read and research more information, as I want my "first born" to be with us as long as possible.

Thanks,
Michelle from Texas

Siouxsie: For the benefit of our other readers, Michelle, we're going to start by explaining how the kidneys work. The kidneys serve as filters for the blood. Blood runs through millions of tiny structures called nephrons, where toxins and waste products are filtered from the blood. The nephrons then produce urine by combining these waste products with water.

Thomas: When the kidneys start to fail, the blood isn't filtered as effectively and a blood test can reveal that toxins are still in the blood. Nitrogen, for example, is one of the major waste products filtered out by the kidneys. The BUN (blood urea nitrogen) level shows how much nitrogen remains in the blood after being filtered by the kidneys.

Siouxsie: The Creatinine (Cre) level also measures waste products that should be filtered by the kidneys. Increases in the BUN and Creatinine level indicate that the kidneys' filtering function is becoming less effective.

Thomas: Your vet may recommend other diagnostic tests to check Mr. Louie's kidneys. A urine sample can be measured for specific gravity. This will tell your vet how well Mr. Louie's kidneys are filtering urine. Failing kidneys will produce a lot of urine but without a lot of waste products in it.

Siouxsie: Your vet may also want to examine Mr. Louie's kidneys with ultrasound or other imaging technology to determine exactly what percentage of his kidneys are working. An ultrasound could also reveal a tumor or other issues.

Thomas: Chronic renal failure (CRF) is a common problem in elderly cats. This is one of the reasons veterinarians often recommend pre-anesthetic testing for senior cats needing surgical procedures. The kidneys and the liver are the organs that filter toxins such as anesthetics out of the body, and if these organs aren't working as well as they should, vets have to be extra careful when giving anesthesia and provide extra support during recovery.

Siouxsie: Renal failure is so common because kidneys age, the nephrons begin to die and are not replaced.

Thomas: Vets estimate that as many as 30% of senior cats have some degree of kidney failure. Most of the time their caretakers don't know this because the kidneys can compensate for loss of function until about 70% of the nephrons are gone.

Siouxsie: Once the cat only has about 25 to 30% of normal kidney function, the cat will start showing symptoms of kidney failure. These include increased thirst and urination, loss of appetite and/or weight loss, nausea and vomiting, a foul urine-like smell on the breath, lethargy and dehydration.

Thomas: Michelle, if Mr. Louie isn't having any of these symptoms yet, it's possible that he hasn't reached that critical 30% or less kidney function level. In that way, you're lucky: the pre-anesthetic test revealed Mr. Louie's declining kidney function early enough that you can provide supportive care that will slow the progression of the disease.

Siouxsie: The bad news is that CRF is a progressive disease. No matter what you do, Mr. Louie's kidneys aren't going to stop aging. But by following your vet's advice and making sure you ease the burden on Mr. Louie's kidneys, you can give him a good quality of life for a long time.

Thomas: To answer your first question, Michelle, blood tests are not easily compromised and are just about the most accurate diagnostic tools your vet has in her repertoire. The "normal range" in blood tests has been determined through years of research and millions of blood tests on cats of all ages, types and lifestyles. So if your vet says Mr. Louie's blood work shows an abnormality, that's because there is an abnormality.

Siouxsie: We're not veterinarians ourselves, so we can't answer your question about what a 0.5 mg/dl increase in Mr. Louie's Creatinine level signifies. If your vet says this is not a large increase, we'd take her word for that. Since we're not vets, it would be terribly irresponsible of us to attempt a diagnosis, particularly since we've never met your cat.

Thomas: If you have questions about Mr. Louie's diagnosis, you can seek out a second opinion; most vets will be glad to share your cat's test results with another vet if that is what you wish. You could also work with a holistic vet to provide nutritional and herbal support. Again, many conventional vets are open to working with complimentary practitioners, as long as those practitioners are licensed and responsible.

Siouxsie: The American Holistic Veterinary Medical Association has a directory of its members and their areas of specialty. They provide listings of practitioners throughout the US and Canada.

Thomas: As for your final question, we'll repeat what we said earlier: If Mr. Louie hasn't been showing symptoms of renal failure, the odds are good that he hasn't reached that critical 70% loss of kidney function. An ultrasound and a urine specific gravity test will give you and your vet more information about that.

Siouxsie: You mentioned that your vet prescribed a special food for Mr. Louie. Vets do have a number of foods they prescribe for certain types of chronic conditions. These foods are specially formulated to support the body's special needs.

Thomas: Most regular "senior formula" cat foods are designed to reduce the risk of kidney failure. By manipulating levels of phosphorus, sodium, protein and essential fatty acids, they provide support and ease the burden on the kidneys. These diets also do not acidify the urine.

Siouxsie: Nearly all the major pet food manufacturers make therapeutic diets for kidney disease. Some even have formulas for early stage kidney failure and late stage kidney failure.

Thomas: Kidney diets are designed to reduce the work load of the kidneys by offering lower sodium, lower protein levels, and a fermentable fiber. As we said earlier, failing kidneys leave nitrogen waste in the blood. These fermentable fibers move some of the nitrogen removal function to the intestines and help ease the strain on the kidneys.

Siouxsie: Most cats with kidney failure lose their appetites, and it can be hard to find a food that is palatable enough to encourage them to eat. If Mr. Louie refuses to eat the prescription food, you can try other kidney support formulas -- with the knowledge and consent of your vet, of course!

Thomas: In her book Complete Care for Your Aging Cat (which we recommend highly), Amy D. Shojai lists several kidney diets that are available: Eukanuba Nutritional Kidney Formula Multi-Stage Renal/Feline; Hill's Prescription Diet Feline g/d (early stage); Hill's Prescription Diet Feline k/d (moderate stage); IVD Select Care Feline Modified Formula; Purina Veterinary Diets, NF Kidney Function Formula; and Waltham Feline Renal Support.

Siouxsie: We're sure this is not an exhaustive list, but we wanted to point out that there are options available if Mr. Louie isn't enjoying his prescription food.

Thomas: To help you in your research, we've found some online resources about feline CRF. The Feline CRF Information Center was started in 1996 by a couple whose beloved cat was diagnosed with CRF. They are lay people, just like you, and the site contains tons of information about CRF and its treatment in language that non-veterinarians can understand.

Siouxsie: Judy's World: Living with a CRF Cat is another site full of information and support for people whose cats are suffering from CRF. Again, this is a lay person's site, so be aware that your vet is going to be the best authority on CRF management and treatment.

Thomas: And here's a page of kidney disease information links from the about.com cats forum.

Siouxsie: Good luck, Michelle. We hope this information has been helpful to you. Give Mr. Louie a pet for us.

Dahlia: And me too! I love being friends with other kitties! I can't wait till I'm big enough to answer questions in the column. Siouxsie and Thomas are my heroes. They're so smart. Especially Thomas, and he's nice to me, too. He licks my head and lets me snuggle with him ...

Thomas: That's Dahlia, the newest member of our kitty family. Mama adopted her about two weeks ago. At the time, Mama was told she was a boy, but she soon found out otherwise. She's pretty OK, I like her.

Siouxsie: I like her well enough, as long as she stays away from my food. And my tail. And my throne. And Mama (when I'm on Mama's lap).

Got a question? Need some advice? E-mail us at advice@paws-and-effect.com. None of the material in this column is meant to be a substitute for regular veterinary care.