Chances are good you're here because your cat has just been given a diagnosis of CRF. And if you're anything like me, you're numb and in a panic all at the same time. Stay strong, and keep your chin up because your cat needs you. CRF is not a death sentence.
In my experience CRF is one of the most treatable conditions out there and with gentle methods i.e. no or minimal drugs and supportive treatments, a cat can enjoy an excellent quality of life for many years.

[Jules' darling boy Tuffy who she lost to CRF ]

The kidneys are an incredibly hard-working set of organs. They contain several thousand microscopic nephrons, which filter and reabsorb fluids in the body. Nephron damage and loss of kidney function can occur due to drugs e.g. Metacam at any time and particularly during surgery, infections, toxins, cardiac output causing decreased blood flow to the kidneys, and possibly as part of the aging process.

Progression of the disease depends on several things, including how much time the kidney has to compensate for nephron damage. Even with 25 percent of its original nephrons remaining i.e. by the time elevated BUN and creatinine (both waste products) are discovered on a blood test, a kidney can continue to function for many years.

Symptoms

Common early symptoms include nausea, poor appetite, dull coat, listlessness, increased thirst, and frequent urination. Sometimes the signs are very subtle and thus easy to miss.

Many of the symptoms of CRF can match those of diabetes and hyperthyroidism. One difference in the case of hyperthyroidism, cats are more likely to have a ravenous appetite, but with no weight gain. A CRF kitty will typically not have a huge or even the same appetite s/he did earlier on in their life.

At a later stage, things to watch out for include bad breath with or without mouth ulcers, hind leg weakness (usually due to potassium depletion/deficiency), high blood pressure (which can cause retinal detachment resulting in blindness), and anemia. In some cases, your vet might be able to feel that the kidneys are small and irregular, though in a smaller % of cases, there might be kidney enlargement.

Prolonged vomiting, and impaired ability of remaining nephrons can lead to metabolic acidosis which can be helped by Slippery Elm, and/or sodium bicarbonate (please be very cautious with this), and Potassium citrate if accompanied by hypokalemia.

Testing

Urine test

I'm a big fan of urinalysis (U/A) because it's non-invasive (no need for cystocentesis if one is not testing for bacterial infection), and can be a useful tool for not just early diagnosis of kidney insufficiency but also for monitoring progression of kidney failure to some extent.

A U/A will show among other things, whether there is excess protein being spilled in the urine, as well as specific gravity (USG) of the urine. In normal cats, there should never be protein in the urine. For raw-fed cats (who typically have more dilute urine anyway due to the high moisture content of meat), a USG of less than 1.03 or so (combined with clinical symptoms and/or blood values such as elevated BUN and Creatinine) becomes a warning sign because it signals decreased filtering ability of the kidneys.

I get U/As for my cats at least every six months because it's so easy to just drop off a sample at my vet's. For $20, I get a sense of my cats' liver, kidneys, and pancreas health, so it's well worth it, IMO. I'm even crazy enough to have purchased a hand-held refractometer for around $35 so in between full U/A from my cats' holistic vet, I can quickly and easily check USG at home for each of my cats on a monthly basis.

You might not be as big a nutter as yours truly, but if you can swing even once a year testing, please consider it. This is even more important after age 7 or 8, although it is not uncommon for cats as young as 2 years of age eating dry food to have failing kidneys. While we're on the subject, please pretty please do not feed your cat that horrible grain-based dehydrated junk, which is about as far removed from cat prey as can be. For a quick read (I promise!) on why, click here.

Blood/serum tests

When it comes to blood work, it only shows raised levels of Blood Urea Nitrogen (BUN) and Creatinine -- both of which are waste products excreted in the urine -- after at least 70-75% of the kidney function is lost. Rule of thumb - if your cat's BUN is higher than 33 or so, and Creatinine is higher than 1.8 - 2.0 Mg/Dl (varies, so please consult your lab's range), less than 25% of kidney function is left. Note: European and Commonwealth e.g. British and Canadian measurements are different so click here or if previous link is not working, then check Merck Vet Manual link here for conversions to US units.

It's best to do a SuperChem profile, which gives not only BUN and Creatinine, but also Phosphorus and Potassium which are important to monitor as well.

In addition, since cats with CRF can be prone to anemia, it's good to get a complete blood count (CBC) which looks at the numbers of white and red blood cells (RBCs). A lower than normal number of RBCs is significant because it often indicates a drop in erythropoiten, a hormone secreted by the kidneys that stimulates RBC production.