Kidney Disease In Dogs And Cats

Chronic Renal Problems Chronic Renal Failure (CRF), Chronic Renal Insufficiency (CRI)

Ron Hines DVM PhD

I wrote this article a number of years ago but little has changed. Please explore these links because there is useful information for you there too:

Update On Kidney Disease Treatment In Dogs & Cats

Hyperthyroidism & Kidney Disease In Cats

The SDMA Kidney Test And Its Value

Special Diets For Kidney Issues    

All of our bodies suffer the wear and tear of time. In people, our hearts are often our weakest organ. In dogs and cats, it is often the kidneys that wear out first.  There is a slow, but steady, loss of kidney function in dogs and cats throughout their life – significant enough to make  chronic renal (kidney) disease the second leading cause of illness in older dogs and cats. The first is arthritis.

What Happens When Your Pet’s Kidneys Begin To Fail?

First, you need to know something about how kidneys work. Kidneys keep your pet’s body free of the wastes that naturally accumulate during metabolism. Veterinarians measure two of them, BUN and creatinine, but there are many more. The kidneys are also continuously scrubbing your dog and cat’s blood free of excess salts and water. When some essential component of your pet’s body is in short supply, its kidneys sense that and do their best to conserve it (not allow it to leave in urine). Your pet’s urine is darker and more odorous when it is dehydrated because its kidneys are letting as little water escape from its body as they can. 

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. No one has counted them in dogs or cats. Each nephron contains a small sieve-like filtering structure called a glomerulus. These glomeruli  keep normal blood proteins and cells in the bloodstream, while allowing extra fluid and wastes to pass through to end up in your pet’s urine. A complicated chemical exchange takes place, as waste materials and water leave the blood and enter the urinary tract. The kidneys also regulate the pet’s body’s acidity. 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 your 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 D3 into its active form, calcitriol . Calcitriol is essential to preserving the proper balance of calcium to phosphorus in your pet’s  bones and blood stream. Vitamin D receptors are present in most if not all cells of the body, but their functions there are poorly understood. In chronic kidney disease the functional areas of your pet’s kidneys become non-functional: scarred or plugged up with leaked proteins and inflammatory cells (casts). Without enough functional tissue, none of the processes I mentioned work satisfactorily.

But My Pet 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 whatever remaining capacity they have to remove waste. This accounts for the excess thirst and urination you have see in your pet. For a while, this compensation keeps it’s body clean enough of wastes to function, but gradually over time, the pet can’t consume enough water to keep its waste levels in check. By the time your dog or cat experiences weight loss, anemia, and abnormal blood work results, over half of its kidney glomeruli have been lost. You pet cannot replace them. Glomeruli never regenerate – at least not with the tools that veterinarians and physicians have today.

What Are Common Signs Of Kidney Disease In My Pet?

The first sign that there is a problem that pet owners usually notice is excessive drinking and urination. At first, it is normal for owners to ignore this. It might just be that your dog wakes you up during the night to be let out or your cat’s litter box is damper than it once was. Your cat or dog’s water bowl might have to be filled more often than it used to. But with time, the pet begin to loose weight and become a more finicky eater. About this time, it is common for the pet’s energy level to decrease. Most veterinarians associate that with metabolic toxin buildup in the dog or cat’s body. They are likely to play less, romp less and sleep more. Often their coat lacks the luster it once had. This is usually the point where concerned owners take them to see their veterinarian. In advanced kidney disease, pets have little interest in eating. Coaxing them to eat with tuna or salmon juice might work for a while. These pets often develop digestive disturbances such as nausea, retching 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 pets have all developed uremia – an intolerably high level of nitrogen-containing metabolic waste products in their blood. Because many of these toxic waste products  contain the azo-molecular grouping of nitrogen, another term for uremia is azotemia.

Why Did This Happen To My Dog Or 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 none of them have been scientifically proven to be true. Regardless of the cause(s), all cases of chronic kidney disease develop similar signs and pass through similar stages. Usually, your veterinarian will just tell you your pet has CRF. This is because, in most cases, there is no way for the veterinarian to determine the 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 dogs and cats early. But with advances in pet nutrition, vaccination, antibiotics and sophisticated surgery, our cats and dogs now live much longer. Nothing lasts forever and I mentioned that every organism has its weakest link. Unfortunately the critical cells of the kidney (podocytes) cannot replace or regenerate themselves as critical cells do in the liver, blood, bone, skin and cornea. Once a glomerulus ages and is lost, it is lost forever. Time is probably the most common cause of kidney failure in dogs and cats.

Polycystic Kidney Disease

Some cats and dogs 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. (read here) It is much less common in dogs, but there are reports of the disease occasionally occur. (read here)

Chronic interstitial Nephritis

Chronic interstitial nephritis is the most common form of kidney damage in older dogs. It occurs less frequently in cats. Nephritis is a pathologist’s 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 present in these interstitial areas. This low-grade, chronic inflammation is thought by some to cause scaring that eventually destroys most of the nephron filters. An acute (sudden) nephritis can occur in dogs that have become infected with leptospirosis. Leptospirosis is diagnosed much less frequently in cats. After the acute phase of this disease, the organism responsible sometimes lingers for long periods of time in a pet’s kidneys and, in some cases, causing chronic nephritis. However, most dogs with chronic interstitial nephritis show no evidence that they were ever infected with leptospirosis. Pets suffering from chronic interstitial nephritis have small, shrunken, hard kidneys due to scarring. If the pet is not too chubby, it is easy for a veterinarian to palpate and identify these shrunken, lumpy, hard kidneys during a routine veterinary exam. Any adult cat or dog that passes through my clinic is likely to get its kidneys palpated.

Over-stimulation Of Your Pet’s Immune System – Chronic Inflammation

Your pet’s kidney glomeruli act as a sieve, straining and filtering all the blood that passes through them. In a typical day the entire blood content of your body passes through your kidneys about 60 times. I assume it is not much different in your dog or cat. Large molecules in the blood have a tendency to become lodged there.  Some of these large molecules are antibodies combined with antigens (immune complexes). Many chronic infectious, allergic and auto-immune diseases of dogs and cats produce these  immune complexes. They include Lyme disease, chronic skin infections, chronic intestinal disease, overactive adrenal glands (Cushing’s disease) and diabetes. The inflammation of chronic gum disease (periodontal disease) is also associated with kidney disease in humans. (read here) Perhaps a similar connection occurs in our dogs and cats. Veterinarians do not know.

The most common form of heart disease in dogs is mitral valve disease. We do not yet know if heart valve disease is a risk factor for kidney disease in dogs or cats. But when bacteria are involved, they have the potential to break loose from heart valves and lodge in the kidneys. (read here

A type of destructive protein sometimes accumulates in the kidneys.  It is called amyloid (amyloidosis). In some cats, this occurs as a genetic disease. But it is also know to occur subsequent to long-term over-stimulation of the immune system. Abyssinian and Siamese cats, shar pei and akita dogs all 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 these diseases, 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. The most common form of autoimmune disease in dogs is the skin form of pemphigus  that tends to occur around the nose, eyes and anus. Those run-away antibodies also pass through your pet’s kidneys. What damage if any that they cause there is unknown. 

Hyperthyroidism In Cats And High Blood Pressure

An overactive thyroid gland or hyperthyroidism is a common problem in older cats. Veterinarians are uncertain why it appears to be  occurring more frequently. But we know that it often occurs in cats concurrently with kidney disease. Hyperthyroidism often masks the early signs of kidney failure that I described because hyperthyroid cats generally drink a lot. 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 can cause your cat’s  blood pressure  to be abnormally high. We also know that high blood pressure leads to kidney failure. That might be why hyperthyroidism and kidney failure go hand-in-hand in cats.

Lower Urinary Tract Disease

Feline Urological Syndrome ( FUS ) is another common disease of cats. In this condition, a pasty grit (struvite or oxalate crystals) irritates and sometimes plugs your cat’s urethra preventing normal urination. When the urethra is partially or completely plugged and the cat cannot pee (even intermittently) urine pressure builds up in the bladder, up theuretertubes to the kidneys, and into the kidneys themselves. Abnormally high urine pressure in the kidneys will slowly destroy them. The condition is called hydronephrosis. However most cats that have lost their normal kidney function do not show the kidney changes associated with hydronephrosis. In dealing with FUS, cats were often placed on diets that were acidic or urinary acidifiers in an attempt to prevent struvite crystals from forming. Some veterinarians believed that the acid urine these diets produced was unhealthy for kidneys and may be one of the reason that kidneys fail. The pH of these prescription diets has been adjusted upward to take this into account.

How Will My Veterinarian Diagnose Kidney Disease In My Dog Or Cat?

The history you give your veterinarian, your pet’s age and the veterinarian’s physical examination of your pet 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 in dogs and cats, see my article on normal blood values).

Your Dog And Cat’s Urine Specific Gravity

When your veterinarian asks you to bring in a urine specimen from your pet, its specific gravity will be checked. This tells your veterinarian how concentrated the urine sample is. Pets that have weakened kidneys have difficulty producing concentrated urine. The lower the specific gravity, the more serious the kidney problem is likely to be. However, anything that causes your pet 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 it rises in the morning and before it has consumed water. For certain analysis, it is better if the veterinarian collects the sample. Urine samples more than 30 minutes old are hardly worth examining.

Urine Protein Content And Microscopic Urine Examination

Failing kidneys leak blood proteins into the urine. Most of this protein is albumin. The most accurate test for kidney issues in not a urine protein test, it is the microalbuminuria test. A high urine protein reading in this test is often an early sign of sudden or long-term kidney damage. The presence of white blood cells and debris in the urine can help veterinarians  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 pets 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 pets 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 pet 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 pet consumes are very high in phosphorus. It’s failing kidneys have difficulty excreting sufficient phosphorus into the urine. An elevated blood phosphorus level is often another sign of failing kidneys. As the ratio of phosphorus to calcium in the blood becomes abnormal, the pet’s bones will weaken. This is why pets in kidney failure need to be fed diets low in phosphorus. Pets 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.

Packed Cell Volume (hematocrits, Hct, PCV)

Your cat and dog’s packed red blood cell volume (PCV) is a measure of possible anemia. When a pet 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 pet’s kidneys deteriorate, not enough of this hormone is produced.

Blood Pressure

You veterinarian may also measure your pet’s  blood pressure . Getting an accurate reading in cats and apprehensive dogs is extremely difficult. Read about that here. It is common for pets with chronic kidney disease to also have abnormally high blood pressure. It is unclear if the high blood pressure is part of the cause of 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. That is called secondary hypertension.

What Treatment Options Do I have For My Pet?

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 pet’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 pet 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

Prescription diets, designed for kidney failure in dogs today are not true low-protein diets. They are lower lower in protein (~2/3 the amount of protein) and sodium found in standard dog foods.  It is even harder to safely lower the amount of protein in cat food. To thrive, cats require more protein than dogs. Manufacturers also  addomega 3 and omega 6 fatty acids and compounds like potassium citrate to counteract body “over-acidity” and these diets are drastically lower in phosphorus. Your pet’s health on protein restricted diets needs to be monitored carefully. Blood tests need to be done periodically to be sure that the pet’s blood protein levels have not dropped too low and that the dog or cat’s body weight remains stable. When you do that, and your pet’s BUN and Creatinine levels drop or remain stable, protein restriction is probably a positive step.  But there are periods in a pet’s ongoing fight with kidney disease when restricting protein might not be a good thing to do. For example, when 7/8th of a group of dog’s kidney was removed experimentally, dogs fed low protein diets actually died sooner.  Cats do not tolerate true low-protein diets well at all.  It is wiser to depend more on added fat and fiber for dilution of the cat’s protein consumption rather than a large amount of added plant carbohydrates. Ketoacids, as sold through body building outlets, can also act as a substitute for dietary protein in certain instances. But I know of no veterinarians that use those type of diets in dogs and cats.

Always make your pet’s dietary changes gradually. 

No matter what you decide to feed, we always want to limit your pet’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 pets ingests is also wise when its kidneys are failing – so commercial-prepared 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 pet’s BUN is over 60 mg/dl, most vets believe that moderately restricting protein in your pet’s diet does become important.

Vitamin Supplements

Pets 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 deficiency.

ACE Inhibitor Medications

An organ as basic as the kidney does not appear to vary much between mammals. Experiments in kidneys disease are most acceptable to animal welfare advocates these days when they are done in rats.  The cells that researches zero in on in declining kidney function are the podocytes , cells in the kidney’s filtering apparatus that underlies its blood-cleansing abilities. Once podocytes loss begins, like a tree, bent to a severe angle by a storm – it will continue to slowly fall even after the wind ceases even though the remaining filers “super nephrons” enlarge (hypertrophy) and work harder. There is considerable evidence that medications called ACE inhibitors can slow that loss.  The ACE inhibitor most often chosen for pets are benazepril  and enalapril If your pet is placed on an ACE inhibitor, it is wise to be sure that its blood creatinine levels do not increase. In later kidney failure when the remaining kidney filters (glomeruli) are filtering way above their normal capacity, ACE inhibitors occasionally drop the kidney’s internal pressure so low that the pet’s uremia actually worsens. The best monitoring test in those situations is a 24 hours creatinine clearance test or another test that estimates your pet’s GFR.

The most common side effect of ACE inhibitors in pets are stomach/intestinal upsets, constipation and weakness do to too low a blood pressure. In those cases, the dose needs to be reduced. Sometimes these side effects can be lessened if you begin these medications at a low dose and gradually increase them to the desired dose.

Phosphorus binders

Certain compounds called phosphate binders can block the absorption of phosphorus from your cat’s foods while it is still within its digestive system. At one time, aluminum hydroxide was suggested. Dietitians now think that more modern products that are free of aluminum are safer. Some common ones are calcium acetate (PhosLo®), sevelamer (Renagel®) and Epakitin®. There are others. ( read here )

Calcitriol

Since pets with advanced kidney disease may not produce adequate amounts of active vitamin D in their kidneys, the preformed compound, calcitriol, has been given to them. It is generally given when your pet’s  blood calcium to  blood phosphorus ratio become significantly abnormal.

Potassium Supplements

Potassium supplements (Tumil K®, etc.) help when the pet’s blood potassium level drops too low. This sometimes helps combat the listlessness and weakness that accompanies advanced kidney failure.

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 bioengineered for humans, dogs and cats eventually cease responding to them. But they might raise your pets PVC for a short time. There is a danger in giving these product. When your pet’s immune system decides to attack human erythropoetin as a foreign protein, it may not only destroys the human erythropoetin that was given – it might also destroys the pets natural erythropoetin. That would make the anemia even worse. I would only consider giving erythropoetin in a last ditch effort to gain a bit more quality time with your pet. I personally would be looking more closely at the quality of life than the extension of life. 

Fermentable Fiber

Fermentable or soluble fiber, when added to a pets 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.

Fluid Administration

There comes a time with all pets 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 pet additional fluids orally or add additional liquid to its food. When that is no longer sufficient, the fluids needs to be give periodically under the pet’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 fluids at home. In most cases, there is no benefit in giving them intravenously. Pets with failing kidneys do need emergency intravenous fluids when they are presented severely dehydrated to veterinarians.

How Much Longer Will My Cat Or Dog Live?

That is completely dependent on the level of toxins in your pet’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 its 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 pets if you are fortunate enough to be able to afford them. They are much more successful in cats than in dogs. 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. 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 pets 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. Dogs do not fare as well with kidney transplants. The biggest obstacle to kidney transplantation in dogs is rejection of the new kidney. Powerful immunosuppressive drugs must be given to the dog for the rest of its life. These drugs have serious side effects of their own. Centers that once performed the procedure on dogs have ceased to do so. But others are always begin programs that attempt to get around the hurdle of rejection in novel ways.

Is Hemodialysis An Option For My Pet?

Hemodialysis, as performed on humans with failing kidneys, is not done frequently in dogs or cats. The veterinary school at the  University Of Florida once released as press report of a successful hemodialysis procedure in a dog. I do not know if other veterinary centers that are attempting it but there probably are some. When veterinarians attempt hemodialysis, they are much more inclined to do so for fixable events such as drug overdoses or toxin consumption than to attempt long-term dialysis to maintain a pet in kidney failure. Perhaps one might use hemodialysis as a temporary delay method until a kidney transplant could be performed on your cat, or perhaps to improve the likelihood of it surviving the transplant surgery when it did get performed. I have never tended to a client cat in that situation.   

I Am Desperate – What About New Experimental Drugs, Homeopathic Remedies And Other Unproven Treatments I Read About On The Internet?

A few of the medications that are currently being tried by veterinarians on pets with kidney failure might some day be proven to be beneficial. The only way veterinarians and physicians make progress in medicine is through experimentation. However the majority of these new treatments will be found not to be helpful. If traditional medications and procedures are no longer helping your dog or cat, there is no harm in trying an experimental therapy. Things that are sold over the Internet to desperate pet owners and that make marvelous claims are always worthless. Some veterinarians are not above offering those dodgy treatments as well. ( read here ) The ones that Google might choose to advertise on my website are no better. I will block any you notice.

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