Kidney Disease In Dogs And Cats

We all suffer the ravages of time. In people, our heart seems to be our weakest organ. In dogs and cats, however, it is the kidney. There is a slow but steady loss of kidney function as our pets age, so much so that chronic renal (kidney) failure is the leading cause of death in dogs and cats.

Pathology Of the Disease:
The functional portion of the kidneys is a small individual filter called a glomerulus. There are thousands of these structures in the normal kidney. Each glomerulus is attached to a tubule to comprise a unit called a nephron. The glomerulus resembles a twisted mass of tiny tubes through which blood passes. The glomerulus first filters larger molecules out of the blood that passes through it. The filter is semipermeable, allowing water and soluble waste to pass through and be excreted as urine. The urine, then passes into the tubules to be concentrated. In kidney disease these glomeruli are scarred and lost or plugged up with proteins and inflammatory cells.

The most common causes of kidney failure in dogs and cats is chronic inflammation of the glomeruli (chronic nephritis) due to causes we do not fully understand. We call this disease chronic interstitial nephritis. At one time we thought that chronic nephritis was associated with feeding a diet too high in protein. This theory is now in doubt. Some degree of nephritis is very common in dogs over the age of eight. Other diseases such as high blood pressure, abnormal protein infiltration (amyloidosis), elevated thyroid hormone (hyperthyroidism), bacterial infection and toxic chemicals can also contribute to chronic kidney disease. All these diseases rob the kidneys of filtering ability, which results in toxic products of metabolism building up in the blood stream instead of leaving in the urine. We refer to this loss of filtering ability as chronic renal failure or CRF. Dogs and cats with this disease produce large volumes of dilute urine in an attempt to cleanse their blood.

When the kidneys begin to fail and toxin concentrations build up in the blood we call the condition uremia. We measure the degree of uremia by measuring the concentrations of two of these toxic metabolites, blood urea nitrogen or BUN and creatinine. The increase of toxins in the blood causes other symptoms besides increased thirst and urination. Uremic patients have poor appetites, decreased ability to produce blood, weight loss and lethargy all due to the circulating toxic metabolites. Phosphorus accumulates in the body of uremic patients and potassium is lost. Blood does not clot normally and ulcers may occur in the digestive tract. Patients often vomit. Neurological signs sometimes occur.

Dogs and cats with CRF may do well for long periods of time by producing large volumes of urine. What the kidneys lack in concentrating (blood cleansing) power they make up for in the production of larger amounts of dilute urine. Two thirds of the kidney’s filtering power must be lost before blood BUN and creatinine levels begin to rise. Normal dog and cat BUN level is 10-20 milligrams/deciliter. Older dogs are often in the thirties or forties. Normal creatinine levels are 0.6 –1.2. It is much more serious when this number begins to rise. We can measure the degree of kidney damage by measuring the specific gravity of the urine the pet produces. Normal dog urine has a specific gravity of 1.020-1.040. Normal cat urine has a specific gravity of about 1.025-1.050. As the glomeruli loose their ability to concentrate the urine, specific gravity falls to as low as 1.008.

Treatment:
When a pet is presented in uremic failure or kidney failure we do what we can to get the remaining kidney glomerula back on line. We do this by administering large amounts of intravenous fluids and sometimes diuretics such as furosemide (Lasix). Because these patients are not eating well we give them vitamins. To lower body phosphorus we used to give them phosphorus-binding medications such as aluminum hydroxide (Maalox). More recent articles state that this is unwise. If their potassium level is low we supplement this ion. Another lost function of the kidneys is the production of erythropoetin, a hormone that directs red blood cell formation. Anabolic steroids such as stanazolol (Winsterol) help restore appetite and counteract anemia through red blood cell formation (erythropoesis). When we are fortunate, these treatments lower the toxic metabolites to a level where the pet can again function for a while. We have no medicine that restores kidney-filtering capacity. We place these pets on special diets that contain moderately restricted amounts of high-quality proteins. These diets are also low in phosphorus and salt. On my website or in this book you will find recipes for home made diets designed for kidney care.

When blood urea nitrogen levels exceed 28 miligrams per decileter and blood creatinine levels exceed 2.5 miligrams per decileter, these and other toxic waste products of metabolism supress red blood cell formation in the bone marrow. When a dog or cat's packed cell volumn or Hct (hematocrit) is less than 20% the pets become noticibly listless and fatigued. The drug Epogen (rhEPO) may increase RBC levels for a while if the cat or dog has inadequate levels of erythropoietin (a hormone produced in the kidneys that stimulates the bone marrow to release RBC's). There isn't much known about it's use in FeLV+ cats, but it's something you and your vet might consider. Because it is a human form of the hormone, cats and dogs eventually produce antibodies which block the effect of human erythropoitin and can cause a serious side effect called red blood cell aplasia. Researchers at Cornell Veterinary School are working on a synthesized form of feline erythropoietin (rfEPO) which should be safe and effective, however it is still in the early stages of development.

Kidney transplants work well in younger cats but dogs tend to reject the new organs. Transplantation in cats is performed at several veterinary schools in the United States. The procedure is very expensive. Hemodialysis as performed on humans is not done frequently on pets because of the time and expense involved.

Some dogs with CRF develop high blood pressure. Enalapril (EnaCARD) , a medicine marketed for heart failure, also lowers blood pressure which helps protect the remaining kidney function as well as decreasing protein loss into the urine..

In pets with CRF the remaining glomeruli leak blood protein into the urine causing a condition called proteinuria. . Smaller proteins, such as albumin and clotting factors are most easily lost. This is why uremic dogs have bleeding problems. One of our tests for CRF is to measure the amount of these proteins that spill into the urine. Protein loosing nephropathy is another term for this condition.

Specific diseases that lead to CRF include polycystic kidney disease in which the kidneys are formed abnormally, renal hypoplasia in which the kidneys are smaller than they should be, familial glomerulonephritis of Bernese mountain dogs, hereditary nephritis of Bull Terriers and bacterial nephritis or infection of the kidneys. Cats with lower urinary tract disease or Feline Urological Syndrome (FUS) that blocks urine flow often develop kidney damage due to increased urine pressure. Dogs with urinary tract stones can also loose kidney function due to increased urine back pressure into the kidneys. Ingestion of toxins such as ethylene glycol antifreeze or large doses of vitamin D also destroy kidney tissue. Certain drugs can also be toxic to the kidneys. These include the sulfonamides, polymyxin B, amphotericin B, chemotherapeutic drugs, gentamycin and amikacin.

Autoimmune disease in dogs and cats can also lead to CRF. This disease is sometimes called systemic lupus erythematosis. Another condition that destroys kidney glomeruli is amyloidosis, a condition in which abnormal proteins clog up the glomeruli. It is particularly common in akitas and shar pei dogs and oriental shorthaired, abyssinians and siamese cats.

Kidney disease in cats is often the cause of elevated blood pressure or hypertension (systolic blood pressure exceeds 160 mm Hg). When this occurs, smaller blood vessels may burst under increased pressure, particularly vessels within the retina of the eye. This can lead to retinal detachment and sudden blindness. To reduce the blood pressure anti-hypertensive drugs should be used. A number of agents called calcium channel blockers and ACE inhibitors are available for treatment of hypertension although many of these are not specifically licensed for cats. Examples of two drugs commonly used are benazepril ( Fortekor®, Lotensin, 0.125-0.25 mg/lb once daily )amlodipine ( Istin®, NORVASC, 0.09 +/- 0.015 mg/lb once daily) and enalapril (Enacard, 0.125-0.25mg/lb once or twice a day).

Recent adive for an 8 month old labrador with inherited kidney disease causing chronic renal failure:

Jake, as you know, has an extremely serious problem. As in humans, dogs can not live very long with failed kidneys such as his. Unfortunately, kidney transplants are very infrequently done on dogs because of rejection problems. They have been often done in cats (see Centers below). Also, there are very few centers that can perform kidney dialysis on dogs. I would check specialty veterinary practices within commuting distance to your home to see if any of them offer this. Jake was born with defective kidneys. It would require an IVP x-ray dye study, ultrasound, or kidney biopsy to refine the diagnosis as to why his kidneys are failing but it would not give your additional treatment options.
Jake's anemia might respond to Winsterol (stanazolol), an anabolic steroid. For larger dogs Winstrol-V can be given at a dose rate of 50mg once a week by injection or tablet..
A medication, calcitriol, is also sometimes helpful during renal failure to increase blood calcium level and prevent bone loss. Also, an angiotensin-converting enzyme (ACE) inhibitor such as Enalpril (Enacard, Vasotec) is often given to increase blood flow through the kidneys, control high blood pressure and protein leakage through the kidneys which also often accompanies renal failure. Also, a gastrointestinal protectant such as famotidine (Pepcid AC) or Cimetidine (Tagamet) could help control the diarrhea.
It is important that Jake receive as much fluid as possible. All the water he will drink on his own plus moistening his food or feeding canned foods and giving him additional dilute chicken or beef broth with a turkey baster in the amount of 20-30ml/pound body weight during the day. You may not be able to give that much but whatever you can will help cleans his blood of waste products that the kidneys no longer can remove. Some people find that giving physiologic saline solution subcutaneously with a 60ml syringe and 20-22 gauge needle is easier than giving it by mouth.
If you prepare or modify intestinal diets to lower the protein content you should also salt the diet with Morton's NuSalt or another salt substitute which is a salt-free, potassium product. Use it as you would salt your own food.
Blood phosphorus tends to go up in renal failure and blood calcium tends to go down. There was an oral phosphate-binding product available without prescription at pharmacies that helped some dogs. One is called Amphogel. I do not know if it is still readily available. Many dogs in renal failure that have low blood calcium also benefit from a calcium supplement such as 2500 mg. of Tums per day or 1800 mg. of Amphojel per day.
If his red blood cell count goes under 30% he might have more energy if he receive erythropoietin injections to stimulate the production of blood. Despite the best treatment available, Jake will not live long. When the quality of his life deteriorates significantly I would discuss putting him down rather than alowing him to linger in a debilitated state.

There has been much progress and activity in the last few years in kidney transplants in dogs. One major problem is that by the time most dogs show signs of renal failure, they are quite old and in these dogs, tissue repair and general vigor after surgery is not what it was when the animal was young. I only know of two centers that have offered renal transplants for dogs, The University of California in Davis and The Veterinary College of The University of Minnesota, St. Paul.

Owners of cats with chronic kidney disease no longer responding to medication now have another option. Veterinarians at the Veterinary Teaching Hospital have developed a successful kidney transplant program that helps cats with this disease, and at the same time gives homes to donor cats who generally come from shelters and rescue groups. Both donor and recipient cats are carefully screened to make sure they are in good health.

The procedure is costly (up to $5000) and requires a commitment to give anti-rejection medication orally twice daily for the rest of the cat’s life. In the thirteen years since the procedure was first performed, however, results have improved dramatically. Recipient survival times have steadily improved. http://www.cvm.ncsu.edu/docs/docsnews.html

Some of the Centers that have offered renal transplants for cats in recent years are:

Companion Animal Hospital, College of Veterinary Medicine
Cornell University, Ithaca, NY (607) 253-3060

University of California-Davis School of Veterinary Medicine
Davis, California (530) 752-1393

Small Animal Hospita, Veterinary Medical Teaching Hospital
University of Florida, Gainesville, FL, (352) 392-4700 Australia

All-Care Animal Referral Center, Fountain Valley, CA
(800) 944-7387, (714) 963-0909

Veterinary Medical Teaching Hospital, School of Veterinary Medicine
University of Wisconsin, Madison, (608) 262-6512

Veterinary Specialty Center, Buffalo Grove, IL, :(847) 459-7535
Vet Surgery Center, Auburn Hills, MI (248) 371-3713

University of Pennsylvania, School of Veterinary Medicine
Philadelphia, (215) 898-4680

North Carolina State University, College of Veterinary Medicine
Raleigh, NC, (919) 513-6588

Dr. Hines 5/10/06 I'm finding conflicting information about the use of Enalapril to treat high blood pressure in dogs with kidney failure. In one article I found on the internet, it said that paradoxically enalapril can cause kidney damage because its vessel constricting activities reduce blood flow to the kidneys and should probably not be used in patients with impaired kidney function. My dog just started on Enalapril yesterday--his blood pressure registered at 300--he's 13 years old. The bloodwork shows no major irregularities (my doctor said unfortunately the blood doesn't show kidney failure until 80% of the kidneys are shot), BUT his urine shows that the kidneys are gradually failing. Have you ever heard of Enalapril accelerating kidney failure and are there alternatives to safely control the high blood pressure? Thank you for your time. (I lost a dog two years ago to kidney failure and I'm trying my best to do things right this time.)

The majority of studies I have read still find enalapril a suitable treatment for high blood pressure in dogs with kidney damage. For safety, one should monitor the kidney function in these dogs closely during the early period of administration and occasionally thereafter.

12/20/06 On your web site, you say “In any of the renal diets, the addition of fermentable fiber may be helpful in controlling uremia. The theory is that the bacteria that ferment this fiber in the intestines utilize some of the excess urea in the pet’s blood stream. “ Can you clarify what you mean by “fermentable fiber”? Thanks! Tara

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