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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 dogs , it is often their kidneys
that wear out first. What Happens When Your Dog's Kidneys Fail? First, you need to know something about the work of the kidneys. Kidneys keep your pet’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 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 their small remaining capacity to remove waste. This accounts for the excess thirst and urination you have seen in your pet. For a while, this compensation keeps it’s body clean enough of wastes to function, but gradually, the pet 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 Pet? The first sign that there is a problem is when your pet begins to drink water and urinate excessively. 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 that its water bowl had to be filled more than it used to. But with time, the pet begin to loose weight and become a more finicky eater. About this time, the dog's energy levels tend to decrease. They play less, romp less and sleep more. Generally, their coat lacks the luster it once had. This is often when pets are first taken by their concerned owner to see their veterinarian. In advanced kidney disease, pets will no longer eat. They often have 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 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 Pet ? 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 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 early. But with advances in pet nutrition, antibiotics and sophisticated surgery, our pets 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 dogs. Polycystic Kidney Disease This problem occurs more frequently in cats. But some dogs were also 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. Breeds that develop the problem most frequently include, blue merle collies, west highland whites, and Australian bull terriers. Chronic interstitial Nephritis Chronic interstitial nephritis is the most common form of kidney damage in older dogs. 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 dog's nephron filters. Acute (sudden) nephritis can occur in dogs that are infected with leptospirosis. After the acute phase of this disease, the organism responsible sometimes lingers for long periods of time in the pet’s kidneys, causing a 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 often easy to palpate and identify these shrunken firm kidneys during a routine veterinary exam. Chronic Over-stimulation Of The Pet’s Immune System Your dog's kidney glomeruli act as a sieve, straining and filtering blood as it passes through it. 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 pets. A type of destructive protein sometimes accumulates in the kidneys. It is called amyloid (amyloidosis). In some dogs, this is a genetic disease. But it is also know to occur subsequent to long-term over-stimulation of the immune system. Shar pei and akita dogs have a higher than normal incidence of amyloidosis which can lead to kidney failure.
Hyperthyroidism And High Blood Pressure An overactive thyroid gland or hyperthyroidism is a very common problem in older cats with kidney damage. Dogs are more fortunate and rarely suffer from hyperthyroidism. It does occasionally occur in dogs and when it does, it is due to a tumor within their thyroid gland. Hyperthyroidism masks the signs of kidney failure, and it is only when your veterinarian resolves your pet's thyroid issues that it becomes apparent that the pet’s kidneys are failing. Lower Urinary Tract Disease Kidney and bladder stones that block the flow of urine cause pressure that slowly destroys the kidneys. This type of kidney damage is called hydronephrosis. Kidney and bladder stones are sometimes dissolved with special diets. 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 Pet? 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, see my article on normal blood values. 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 cannot produce 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. 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 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 dog’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 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 pet’s packed cell volume 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 dog’s blood pressure. 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. This 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 Diets 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. All commercially available kidney diets have had their protein content adjusted upward based on these results. We still want to limit your dog'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 Dogs 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 kidneys. They are used frequently in human medicine to lower high blood pressure and aid in heart disease. One you may be acquainted with is enalapril. Your veterinarian may suggest an ACE inhibitor - particularly if high blood pressure in your pet 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 pet’s blood phosphorus level under control. Calcitriol Since pets with advanced kidney disease may not produce adequate amounts of active vitamin D in their kidneys, the preformed compound, calcitriol, can be given to them. It is generally given when blood calcium/phosphorus levels and ratios become abnormal. Potassium Supplements Potassium supplements (Tumil K, etc.) help when the dog’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 engineered for humans , dogs 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 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 dogs 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 with a turkey baster 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 Long Will My Pet 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 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. However, they are much more more successful in cats than in dogs. Success rates for transplant surgery generally go up as specific veterinary centers gain more and more experience with procedures. Successful transplantation surgery in dogs is still in its infancy. The biggest obstacle to kidney transplantation in dogs is rejection of the new kidney. Powerful immunosuppressive drugs must be given for the rest of the pet's life. These drugs have serious side effects of their own. Centers that once attempted to 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. 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. Is Hemodialysis An Option For My Pet? Hemodialysis, as performed on humans with failing kidneys, is not done frequently in pets. In September of 2008, the veterinary school, University Of Florida released as press report of a successful hemodialysis procedure on a dog. I do not know if other Centers are attempting it. The University of California Veterinary School, Davis is often a leader in pioneering research of this kind. What About New Experimental Drugs, Homeopathic Remedies And Other Unproven Treatments? Undoubtedly, some of the medications that are currently being tried by veterinarians on dogs 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. |
