Ron Hines DVM PhD

All of our bodies suffer the wear and tear of time. In people, our hearts are often our weakest organ. In cats, it is often the kidneys that wear out first.

What Happens When Your Cat's Kidneys Fail?

First, you need to know something about the work of the kidneys. Kidneys keep your cat’s body free of the wastes that accumulate during metabolism. They are continually scrubbing the blood free of excess salts, water and metabolites.

The actual removal of wastes occurs in tiny systems within the kidneys called nephrons. There are almost one million of these structures in a single human kidney. Each nephron contains a small sieve-like filtering structure called a glomerulus. These glomeruli (plural form) keep normal blood proteins and cells in the bloodstream, while allowing extra fluid and wastes to pass through to end up in the pet’s urine. A complicated chemical exchange takes place, as waste materials and water leave the blood and enter the urinary system. The kidneys also regulate the body’s acidity and, through regulation of body salt content, they help control blood pressure.

Cells associated with healthy nephrons produce an important hormone called erythropoietin and and enzyme called renin. Erythropoietin is necessary for the pet’s body to produce and maintain red blood cells while renin activates another hormone (angiotensin) to helps control blood pressure. In addition, healthy kidneys are required to process vitamin D into calcitriol to preserve calcium for bones and for normal calcium balance in the body.

In chronic kidney disease these glomeruli are scarred and lost, or plugged up with proteins and inflammatory cells. Without enough functioning glomeruli, none of the processes I have mentioned work normally.

But My Cat Is Still Producing Plenty Of Urine – More Than Before !

The animal body is marvelous in sensing when it has a problem. In an attempt to keep the body waste-free, your pet’s kidneys work overtime, using their small remaining capacity to remove waste. This accounts for the excess thirst and urination you have seen in your cat. For a while, this compensation keeps it’s body clean enough of wastes to function, but gradually, the cat can not consume enough water to keep waste levels in check. By the time your pet experiences weight loss, anemia, and abnormal blood work results, over half of its kidney glomeruli have been lost. You pet can not replace them.

What Are The Signs Of Kidney Disease In My Cat?

Cats with kidney disease tend not to groom themselves as well as they used to. Another early sign that there is a problem is when your cat begins to drink water and urinate excessively. At first, it is normal for owners to ignore this. It might just be that your cat's litter box is damper and smellier than it used to be or that its water bowl had to be filled more than before.

But with time, the pet will begin to loose weight and become a more finicky eater. About this time, its energy levels tend to decrease. These cats play less, romp less and sleep more. This is often when cats are first taken by their concerned owner to see their veterinarian.

In advanced kidney disease, these cats just peck at their food. They often gag as with fur balls and may have digestive disturbances such as nausea and diarrhea. Their water intake decreases and they become dehydrated. They may stand over their water or food bowl without attempting to eat or drink. These cats have developed uremia – an intolerably high level of nitrogen-containing metabolic waste products in their blood. Because these toxic waste products all contain the azo-molecular grouping of nitrogen, another term for uremia is azotemia.

Why Did This Happen To My Cat ?

Veterinarians know the things that make a pet’s kidneys fail suddenly. We are much less certain why they fail gradually. Many causes have been discussed that seem logical – but few of them have been proven to be true. Regardless of the cause, all cases of chronic kidney disease develop the same signs and pass through the same stages. Usually, your veterinarian will just tell you your cat has CRF. This is because, in most cases, there is no way for the veterinarian to determine the original cause.

The Wear And Tear Of Time

There was a time – not so long ago – when infectious diseases and dietary deficiencies ended the lives of cats early. But with advances in pet nutrition, antibiotics and sophisticated surgery, cats now live much longer. Nothing lasts forever and every organism has its weakest link. Cells of the kidney cannot replace or regenerate themselves as they do in the liver, lungs, bone and skin. Once a glomerulus ages and is lost, it is lost forever. This is probably the most common cause of kidney failure in cats.

Polycystic Kidney Disease

Some cats were destined from birth to loose kidney function too early in life. These pets inherited genes that cause fluid-filled sacks (cysts) to form within their kidneys. As these cysts gradually grow in size, they crowd out and destroy the functional tissue (glomeruli) within the pet’s kidneys. This is an inherited problem in certain purebred cats. It is a less common cause in our run-of-the-mill household cats.

Chronic interstitial Nephritis

Chronic interstitial nephritis is the most common form of kidney damage in older pets. It is the end result of many different inflammatory processes - not just one. Nephritis is a term for inflammation of the kidneys. The tissue that surrounds the nephron filters is called the interstitial tissue. It is the matrix that suspends the nephrons - much like stars are suspended in space. Pathologists that examine kidney tissue from pets with failing kidneys have noticed that many have a higher than normal number of inflammatory cells invading this area. This low-grade, chronic inflammation is thought to cause scaring that eventually destroys most of the nephron filters.

Cats suffering from chronic interstitial nephritis have small, shrunken, hard kidneys due to scarring. If the cat is not too chubby, it is easy to palpate and identify these shrunken firm kidneys during a routine veterinary exam. Some veterinarians associate chronic interstitial nephritis in dogs with possible exposure to leptospirosis-carying rodents. Leptospirosis is very rare in cats and is not likely to account for this type of chronic kidney damage in felines. In fact, cats are genetically resistant to leptospirosis - probably due to relying on rodents as a food source.

Chronic Over-stimulation Of The Pet’s Immune System

Your cat’s kidney glomeruli act as sieves, straining and filtering blood as it passes through them. Very large molecules in the blood have a tendency to collect there and appear to slowly damage the kidney’s filtering-ability. Some of these large molecules are antibodies combined with antigens (immune complexes). Many chronic infectious and auto-immune diseases produce immune complexes. These include lyme disease, chronic skin infections, chronic intestinal disease, overactive adrenal glands and diabetes.

Chronic gum disease (periodontal disease) is associated with kidney damage in humans. It is associated with heart disease in dogs. We do not yet know if it is a risk factor for kidney disease in cats. It is another reason for your to keep your cat's teeth clean.

A type of destructive protein sometimes accumulates in the kidneys. It is called amyloid (amyloidosis). In some cats, this is a genetic disease. But it is also know to occur subsequent to long-term over-stimulation of the immune system. Abyssinians and Siamese cats have a higher than normal incidence of amyloidosis which can lead to kidney failure.

A similar form of kidney damage in pets occurs in auto-immune diseases that are similar to lupus in humans. In this disease, run-away antibodies are produced against the pets own body. In some cases, these antibodies are directed at the pet’s kidneys themselves, in others, they may only accumulate there causing physical damage.

Hyperthyroidism And High Blood Pressure

An overactive thyroid gland or hyperthyroidism has become a very common problem in older cats. You can read my article on this condition. We are uncertain why it is occurring more frequently, but we know that it often occurs concurrently with kidney disease. Hyperthyroidism often masks the signs of kidney failure, and it is only when your veterinarian resolves your cat’s thyroid problem that it becomes apparent that the cat’s kidneys are failing.

We know that hyperthyroidism may cause your cat’s blood pressure to be abnormally high. We also know that high blood pressure leads to kidney failure. This is probably why hyperthyroidism and kidney failure go hand-in-hand in cats.

Lower Urinary Tract Disease

Feline Urological Syndrome (FUS) is another disease that has become very common. In this condition, a pasty grit (struvite crystals) irritates and sometimes plugs the cat’s urethra, preventing normal urination. When the urethra is partially or completely plugged and the cat cannot pee, urine pressure builds up in the bladder, up the tubes to the kidneys (ureters), and into the kidneys themselves. Abnormally high urine pressure in the kidneys slowly destroys them. The condition is called hydronephrosis. However most cats that loose their normal kidney function do not show the kidney changes associated with hydronephrosis. In dealing with FUS, cats are often placed on diets that are very acidic, in an attempt to prevent struvite crystals from forming. Some veterinarians believe that the acid urine these diets produce is unhealthy for the kidneys and may be one reason that they fail. The pH of these diets has recently been adjusted upward to take this into account.

How Will My Veterinarian Diagnose Kidney Disease In My Cat?

The history you give your veterinarian, your pet’s age and the veterinarian’s physical examination of your cat may make your veterinarian suspect a chronic kidney problem.

As kidneys scar, they become hardened, small and lumpy. In lean pets, they have a characteristic feel when felt through the abdominal wall. In these cases, and when a diagnosis is unclear, your veterinarian will run tests. Blood and urine tests that warn of kidney damage are included in all standard laboratory examinations. When your pet feels poorly and the cause is uncertain, these are the first tests your veterinarian will run. For normal results, see my article on normal blood values.

Urine Specific Gravity

When your veterinarian asks you to bring in a urine specimen from your cat, its specific gravity will be checked. Placing some Saran wrap over the cat's litter might makes urine collection easier for you. There are also special cat litters sold to aid in urine collection. For certain analysis, it is best if the sample is collected by your veterinarian. Specific gravity measurement tells your vet how concentrated the urine sample is. Cats that have weakened kidneys cannot produce concentrated urine. The lower the specific gravity, the more serious the kidney problem is likely to be. However, anything that causes your cat to drink excessively will also lower urine specific gravity. That is why it is wise to collect your pet’s urine specimen as soon as possible after you get up in the morning ,before the cat has consumed water.

Urine Protein Content And Microscopic Urine Examination

Failing kidneys leak blood proteins into the urine. Most of this protein is albumin. A high urine protein content is often an early sign of sudden or long-term kidney damage. The presence of white blood cells and debris in the urine help veterinarians tell the difference between sudden (acute) and chronic (long-term) kidney disease.

Blood Urea Nitrogen (BUN)

Blood urea nitrogen, a waste product of metabolism, rises in the blood of cats with failing kidneys. It’s level stays within a relatively narrow range in the blood of healthy pets. BUN level in the blood of ill cats begins to rise when not enough healthy kidney tissue remains to excrete it into the pet’s urine. The higher its level in the blood - the more serious the kidney problem is likely to be. Blood urea nitrogen and creatinine levels are the prime way veterinarians decide if their treatment of kidney disease in your cat is working. You will have many of these tests run on your pet during therapy.

Blood Creatinine Level

Creatinine is a protein metabolite of muscle that tends to rise and fall in tandem with BUN. Creatinine-determination is a more sensitive test for kidney disease then BUN-determination because blood levels of creatinine fluctuate less than urea nitrogen in response to a pet’s being dehydrated or consuming a high-protein meal. So BUN and Creatinine tests are almost always run together. The results are often expressed as a BUN:Creatinine ratio.

Blood Phosphorus & Calcium Determination

Phosphorus is one of the mineral constituents of blood. The foods your cat prefers are very high in phosphorus. It's failing kidneys have difficulty excreting sufficient phosphorus into the urine. An elevated blood phosphorus level is another sign of failing kidneys. As the ratio of phosphorus to calcium in the blood becomes abnormal, the cat’s bones will weaken. This is why pets in kidney failure need to be fed diets low in phosphorus. Cats with kidney damage may also loose their ability to produce calcitriol. When this occurs, they can no longer absorb sufficient calcium from the foods they eat.

Potassium

Proper internal levels of potassium are very important to your pet's well being. When a pet’s kidneys fail, its body potassium levels rise. This problem, called hyperkalemia causes generalized fatigue, nausea and an irregular, slow heartbeat that can be life threatening. However, when pets with advanced kidney disease loose their appetites, their blood potassium level can fall dangerously low. Picky cats often dislike the taste of commercial diets that are formulated for kidney disease. It is very important that they eat. If they do not like the taste of the food your animal hospital provides - make the diet yourself. Recipes are on this page.

Packed Cell Volume (hematocrits, Hct, PCV)

Your cat's packed cell volume is a measure of possible anemia. When a cat with kidney failure has a PCV that is abnormally low, it is not manufacturing sufficient red blood cells. One of the hormones involved in red blood cell manufacture is produced in the kidneys. It is called erythropoetin. When your cat’s kidneys deteriorate, not enough of this hormone is produced.

Blood Pressure

You veterinarian may also measure your cat’s systolic blood pressure. This is the first number - the second, or diastolic pressure, is difficult to obtain. It is common for cats with chronic kidney disease to have abnormally high blood pressure. It is unclear if the high blood pressure is part of the cause of the cat's kidney damage, or the result of kidney damage. High blood pressure is known to damage the kidneys – but kidney disease is also known to elevate blood pressure. This is called secondary hypertension.

What Treatment Options Do I have For My Cat?

In the future, we may be able to regenerate failing organs. But for now, there is no known way to mend damaged kidneys. What veterinarians can do is to try to slow the rate at which your cat's kidney tissue is lost, and deal with the side effects of the loss. Kidney failure is progressive – that means that with time it will get worse. The key to gaining time for your cat is to use the its remaining kidney tissue as efficiently as possible. We try to do this through diet, medications and, when necessary, fluid injections (diuresis).

A Special Diet

You will find more information on diets for kidney disease in another article of mine. Veterinarians were taught in schools that protein levels should be restricted (low) when feeding pets with damaged kidneys. This seemed to make sense because less meat protein should produce less urea and creatinine for the kidneys to have to remove. The National Kidney Foundation still recommends that people restrict their intake of protein when they have kidney disease.

However, more recent studies in dogs suggest that low protein diets may do more harm than good for our pets. All commercially available kidney diets have had their protein content adjusted upward based on these results.

We still want to limit your cat's consumption of phosphorus. The foods naturally highest in phosphorus are the common high-protein foods, meat, poultry, fish, dairy products, peas and beans.

Limiting the amount of sodium your cat ingests is also wise when its kidneys are failing - so commercial-prepared feline kidney diets limit the amount of sodium-rich ingredients in their foods. They also add omega-3 and omega-6 fatty acids that are found in cold-water fish and fish oils combined with flax seed.

In advanced kidney disease, when your cat's BUN is over 60 mg/dl, most vets believe that moderately restricting protein in your pet's diet does become important.

Vitamin Supplements

Cats with kidney problems often have poor appetites, weight loss and anemia. They may suffer digestive disturbances as well that could limit the absorption of vitamins. So B-vitamins are often given as appetite stimulant and to ward off any deficiencies.

ACE Inhibitors

ACE inhibitors are medications that allow blood to flow more freely through the cat's kidneys. They are used frequently in human medicine to lower high blood pressure and to aid in heart disease. One you may be acquainted with is enalapril. Your veterinarian may suggest an ACE inhibitor for your cat - particularly if high blood pressure is confirmed. Some veterinarians prescribe ACE inhibitors in the hope that it will slow the progression of kidney failure even before blood pressure rises. This seems to be the case in humans. Given in the proper amount, they have very few side effects.

Phosphorus Binders

In advanced kidney failure, phosphate binders, such as Amphojel (aluminum hydroxide, Maalox) are helpful to keep the cat’s blood phosphorus level under control.

Calcitriol

Since cats with advanced kidney disease may not produce adequate amounts of active vitamin D in their kidneys, the pre-formed compound, calcitriol, can be given to them. It is generally given when your cat's blood calcium/phosphorus levels and ratios become abnormal.

Potassium Supplements

Potassium supplements (Tumil K, etc.) help when the cat's blood potassium level drops too low. This sometimes helps combat the listlessness and weakness that accompanies advanced kidney failure. Suspect low potassium (hypokalemia) when your cat does not eat adequately to maintain its body weight.

Erythropoetin – Red Blood Cell Growth Factors

Sold as Epogen, Betapoietin or Eporel, these compounds encourage your pet to produce red blood cells and so combat anemia. Because these compounds were engineered for humans , cats eventually cease responding to them. But they often do raise the pets PVC for a time. There is a danger in giving this product. When the pet's immune system decides to attack human erythropoetin as a foreign protein, it not only destroys the human erythropoetin that was given - it also destroys the pets natural erythropoetin. So it can make the anemia even worse. It should only be used as a last ditch effort.

Fermentable Fiber

Fermentable or soluble fiber, when added to a cat's diet, also helps remove toxins from its body. Because of this, it is often an ingredient in commercial diets sold to manage kidney failure in pets. In these diets, the source is sugar beet pulp. It is sold in quantity to stables as a horse feed additive. Too much fermentable fiber in your cat's diet will cause diarrhea and flatulence. This type of diarrhea is a mess - but not a hazard to your cat's health.

Fluid Administration

There comes a time with all cats when they no longer drink enough water on their own to fully utilize their remaining kidney capacity. Early in this period, you can give your cat additional fluids orally with a turkey baster or add additional liquid to its food. Leaving a faucet dripping sometimes encourages drinking as do multiple water bowls.

When that is no longer sufficient, the fluids needs to be give periodically under the cat’s skin by injection. The effect is called diuresis. Its effect in flushing out lowering blood toxins from your pet can be dramatic. Many owners learn how to administer these subcutaneous injections of sterile fluids at home. It causes the cat very little pain or discomfort if it is administered at body temperature, slowly in multiple locations. In most cases, there is no benefit in giving fluids intravenously. Cats with failing kidneys do need emergency intravenous fluids when they are presented severely dehydrated to veterinarians.

How Long Will My Pet Live?

That is completely dependent on the level of toxins in your cat’s blood. Pets with blood creatinine levels below 2.8 mg/dl usually do well for long periods. Pets with blood creatinine levels of up to about 4 mg/dl have also survived happily for many years with appropriate treatment. But when your pet's creatinine levels exceed 5, its quality of life has become quite poor. Level of 5 and above mean that 80-90% of their kidneys have been destroyed. It is possible to keep these pets alive – but I question the kindness of doing this. Your pet loves you very much. But it is a two way street - it is relying on you to end its life peacefully and humanely when the right time comes.

Kidney Transplants

Kidney transplants are an option for cats if you are fortunate enough to be able to afford them. They are much more successful in cats than in dogs, but not as successful as in humans.

Currently, a little more than half of the cats that have kidney transplants survive six months. Of those that do, many have lived an additional three years. The longest servivor I know of lived over 8 additional years. Success rates for transplant surgery generally go up as specific veterinary centers gain more and more experience with procedures. Transplantation surgery in cats is still in its infancy.

Success rates vary from one veterinary center to another. It is not just the expertise of the surgeons that accounts for this. Some Centers are willing to try transplant surgery on cats that are already seriously ill. In those cases, the overall success rate will be lower than at Centers that confine their surgery to more healthy pets. In general, cats with creatinine levels under 10 are the best candidates.

Is Hemodialysis An Option For My Cat?

Hemodialysis, as performed on humans with failing kidneys, is not done frequently in pets. A similar blood-cleansing effect can be obtained through peritoneal dialysis in which fluids are injected, and then removed from your pet's abdomen. Performing hemodialysis, as done in humans, would be much harder due to the cat's small size.

What About New Experimental Drugs, Homeopathic Remedies And Other Unproven Treatments?

Undoubtedly, some of the medications that are currently being tried by veterinarians on cats with kidney failure will prove to be beneficial. The only way we make progress in medicine is through experimentation. However, as in the case with every disease of humans and animals, the majority of these new medications will be found to not be helpful. If traditional medications and procedures are longer helping your pet, there is no harm in trying an experimental therapy. Things that are sold over the Internet with marvelous claims to desperate owners are always worthless.

What Options Are On The Horizon?

The best way to learn of new advances in treating your cat is to visit the Feline CRF Information Center.