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Kidney (Renal) Disease in Cats




Overview
Prevalence
Causes/Transmission
Contributing Factors
Clinical Signs
Diagnosis
Treatment
Prognosis
Prevention

Overview
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Chronic kidney disease is a relatively common disorder in cats, especially geriatric cats. Renal (kidney) insufficiency or renal failure occurs when the kidneys are no longer able to perform their normal function of removing waste products from the blood. The former is the early stage of the latter.

Renal failure is not the same as the inability to make urine. In fact, most cats with renal failure are producing large volumes of urine in an attempt to remove the waste products that have accumulated in the blood. This apparent contradiction between the large volume of urine produced and declining kidney function is often a source of confusion for owners.

Typically, renal failure comes about as the kidneys slowly undergo aging or degenerative changes, but in young cats it may be due to congenital or hereditary disease. (Less commonly, it may be due to cancer involving the kidneys, and this may occur at any age.) Renal insufficiency/failure is a process that usually develops over months to years. Initially, there may be no apparent signs, and the cat's blood work is normal. However, there are irreversible microscopic changes underway in the aging kidney. Eventually, the kidneys will begin to shrink because of scar tissue and will become small and hard. By this time, there are usually signs of progressive renal disease, and the lab work will indicate associated changes.

The kidneys are basically filters that selectively keep certain compounds in the blood, while allowing unnecessary waste products to escape into the urine. When aging causes the filtration process to become progressively less effective, the kidneys become less able to concentrate and conserve the water in the urine. This is the reason that the cat with kidney failure is producing a large volume of dilute urine. Because of the loss of excessive fluid through the urine, the cat is obligated to drink more water to avoid becoming dehydrated. This is called a compensatory change.

Thus, the typical clinical signs of renal failure include increased water consumption (polydipsia) and increased urine production (polyuria).

Prevalence
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Various clinical studies have evaluated the prevalence of renal failure in cats. For most cats, onset of clinical signs begins anywhere from 7-12 years of age. However, the prevalence of overt kidney failure is highest in cats older than 15 years of age. One study found that approximately 30% of cats over 15 years of age had some degree of chronic renal insufficiency or failure. Now that cats are living so much longer than they were 20-30 years ago (due to indoor lifestyle, better nutrition, better veterinary care, etc.), we see much more renal insufficiency, because cats are in essence living long enough to experience these age-related changes to this vital organ.

The frequency of renal failure in male cats is essentially the same as for female cats.

Causes/Transmission
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Chronic renal failure in cats is technically called chronic tubulointerstitial nephritis. This term essentially describes a microscopic finding and is not specific for a particular cause. In most cats, a specific cause for renal failure cannot be determined. In some cats, renal failure is the end result of several diseases or insults to the kidneys over a prolonged period of time. In others, as noted above, the degenerative changes are simply seen with aging, just as they are with people.

Contributing Factors
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At the present time, there are several contributing factors identified that may hasten progression of renal disease:

  1. Hyperthyroidism (overactive thyroid glands). This hormonal disease is relatively common in older cats. Hyperthyroid cats are often hypertensive (have high blood pressure), and this results in increased blood flow through the kidneys. As mentioned above, extra blood flow helps the aging kidney maintain function. With treatment of hyperthyroidism, blood pressure normalizes and the extra blood flow to the kidneys is no longer present. This can cause a sudden decompensation of kidneys with already marginal function. On the other hand, the long term effects of hyperthyroid disease like high blood pressure can cause progression of renal failure.
  2. Urinary tract infection. Infection in the kidneys and/or bladder may be present without any apparent signs. To prevent bacteria from further damaging the kidneys, cats with kidney failure should have the urine checked for the presence of bacteria at least every 6 months.
  3. Dental disease. Recent studies have shown that chronic dental disease can lead to the introduction of oral bacteria into the blood stream. These bacteria go on to "seed" various organs, including the kidneys, causing kidney and bladder infections.
  4. Toxins. Substances such as ethylene glycol (anti-freeze), lilies, etc. are extremely toxic to the kidneys if ingested.
  5. Diabetes Mellitus. The microvascular changes that can be seen with diabetes can have a profound effect on the kidney vasculature, and thus kidney function.
  6. Stress. Chronic stress can be harmful to overall health, including the health of the kidneys.
  7. Hypertension.  Elevated blood pressure can damage the small blood vessels that go into each individual kidney unit called a nephron.  This can cause nephron death and when enough nephrons die, kidney dysfunction occurs.

Clinical Signs
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As described above, the classic signs of renal failure are increased urine output and a compensatory increase in water intake (thirst). Also, with more advanced renal failure, other signs may include loss of appetite, weight loss and a poor haircoat, depression, vomiting, diarrhea, and very bad breath. Occasionally, ulcers will be found in the mouth. A heart murmur may be present when the anemia of renal failure develops or if the cat has kidney-associated hypertension.

High blood pressure may be found in cats with failing kidneys. Sustained high blood pressure can cause some cats to have a stroke, or the retinas of their eyes to detach. These situations result in sudden blindness and loss of equilibrium.

Diagnosis
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The diagnosis of renal failure is made by determining the level of two waste products in the blood, blood urea nitrogen (BUN) and blood creatinine, and urine specific gravity. Urine specific gravity is obtained from a urine sample. It helps assess the ability of the kidneys to "do work." The normal cat has very concentrated (yellow) urine (high specific gravity), whereas the cat with renal failure has dilute, watery-appearing urine (low specific gravity).

When the BUN and creatinine reach certain levels, they are very specific indicators of renal failure. However, the problem with these tests is that they do not become abnormal until late in the disease. Over 75% of kidney function must be lost before the test results are substantially elevated.

There are tests now available that determine the presence of microscopic amounts of protein in the urine which, if found in excess, may indicate renal insufficiency at a much less advanced stage than do the previously mentioned urine specific gravity, BUN or blood creatinine. Excess protein in the urine that is persistent may be harmful to the kidneys and is associated with a poorer prognosis.

Other laboratory abnormalities can be seen with varying degrees of renal failure. High phosphorus and low potassium can often be seen. Some cats have elevations in their blood calcium levels. Anemia is a common abnormality because the kidneys produce a hormone that stimulates red blood cell production. As the kidneys decline, they produce less and less of the hormone, causing progressive anemia. Additionally, kidney disease associated ulcerations in the intestinal tract may cause microscopic GI bleeding, which can also contribute to anemia as well as adversely affect appetite.

Performing urine cultures on cats with CKD is important. Since the urine is dilute, it can make identification of bacterial in the urine difficult.  Thus, bacterial urinary tract infections can be missed by running just a simple analysis of the urine. A culture is the 'gold standard' test for determining if a kidney infection is a cause or complicating factor in the kidney failure.

Treatment
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Treatment depends on the various manifestations and severity of each individual cat's renal failure. Short of a kidney transplant, there is no "cure" for CKD. Treatment strategies, therefore, focus on providing general support for the feline patient that is aimed at helping maintain a good body weight and an acceptable and even normal quality of life. In other words, our goals in treating CKD are to manage the disease, rather than to "cure" it. The aggressiveness of the management strategy will vary depending on the patient's severity of CKD, the owner's willingness and ability to provide treatment and most importantly the cat's willingness to accept and respond favorably to the treatment.

Fluid Therapy
This is a mainstay of renal failure treatment. IV fluids may be required for advanced cases of renal failure, especially when first diagnosed, but mild to moderate renal failure can often be treated with subcutaneous fluid administration at home (fluids administered under the skin by the owner).

Renal Diets

These are therapeutic prescription diets are low in both protein and phosphorus. The decreased protein content may help retard the progression of the kidney failure. Phosphorus restriction is probably the most important component of the renal diet(s). As renal failure advances, the kidneys are less able to eliminate phosphorus. This can lead to a calcium/phosphorus imbalance and eventually mineralization of the kidneys, causing further progression of the disease. These diets are available only through your veterinarian.

Antacid medication
Uremic toxins seen with kidney failure cause increased production of gastric acid and can lead to nausea, inappetance, and even ulcers throughout the gastrointestinal tract.

Potassium Supplementation
Potassium is often low in cats with renal failure because the kidneys do not retain it as they normally would. Low potassium is associated with decreased appetite, weakness and lethargy. Veterinary potassium supplements are available in tablet, gel, or powdered formulations for cats.

Vitamin Supplementation
A general multivitamin with high levels of iron is preferred since many of these cats are anemic and iron may help with anemia. Additionally, since many of the water-soluble B vitamins are lost with the excess volume of urine that these cats produce, a quality supplement is always a good idea.

Antiemetics (anti-vomiting medication)
When acid-blockers fail to control vomiting, stronger anti-vomiting medication may be needed.

Phosphorus Binder
This is used when a renal diet alone fails to keep the blood phosphorus levels under control or the cat will not eat a renal diet (and in the more advanced stages of renal failure, even cats that will eat the prescription renal diets may need phosphorus binder medication). These medications must be given with food in order to be effective.

Anabolic Steroids
These can help with anemia, appetite, and weight gain but can be associated with side effects (liver enzyme elevations).

Blood Pressure Medication
High blood pressure, both systemic as well as within the kidneys, is often seen in cats with renal failure, and can be detrimental to the kidneys if not treated.

Erythropoietin (EPO)/Darbepoetin. This is used when anemia is progressive and is not responsive to vitamins or anabolic steroids. It directly stimulates the bone marrow to produce red blood cells. Presently feline-derived EPO is not commercially available, so human EPO (usually Darbepoetin) is used. Unfortunately, some animals will eventually develop autoantibodies and become profoundly anemic due to arrestment (slowing down) of red blood cell production. Others may develop seizures. Because the side effects of EPO are potentially life-threatening and do occur in a small percentage of cats, this drug is usually not instituted unless all other medications that improve the anemic state have failed.

Calcitriol
This medication helps prevent or control overactive parathyroid gland function which commonly occurs with CKD. By controlling parathyroid levels, cats often feel better. Additionally, if calcium and phosphorus are kept in balance (a function of the parathyroid gland), it helps to prevent calcification of kidneys and further progression of CKD.

ACE Inhibitors
These medications are designed to decrease blood pressure within the kidneys and decrease protein loss.

Appetite Stimulants/Feeding Tubes
Either of these may be helpful in those cats who seem OK otherwise, but whose overall caloric intake is less than what it needs to be (which in turn is detrimental to the kidneys - lack of adequate protein is worse than excess).  Nutrition is critical in helping CKD cats to feel their best.  Our goal is to assure that these kitties eat enough to maintain their body weight and/or slow the progression of any unintentional weight loss.

Kidney Transplants
This procedure is being done at a few locations in the country. Generally, the cat must still be in good condition and not ill from the kidney failure in order to be accepted for a transplant. The cat cannot have life threatening diseases or other diseases that might complicate the transplant. Multiple pre-transplant tests are required prior to referral for a transplant in order to determine if the patient is an acceptable transplant candidate.

Many transplant centers require that the owner adopt the cat that has donated a kidney for the procedure. Some find this undesirable; others find it very rewarding. Also, multiple medications must be given daily for the duration of the cat's life; the antirejection drugs can be extremely expensive. Repeated blood tests are required to monitor function of the transplanted kidney and to monitor blood levels of the antirejection drug. The cost for the transplant procedure, medicines, blood monitoring, and follow up care can ultimately add up to thousands of dollars.

Prognosis
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Prognosis can depend on response to the initial stage of treatment and your ability to perform the follow-up care. However, we encourage treatment in most situations because many cats will respond and have the potential for good quality life for months to years.

Prevention
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For the most part, renal failure is not a preventable disease. It occurs as a consequence of aging. However, known causes that can be prevented or managed include the following:

  1. Urinary tract infections should be identified and treated.
  2. Renal status should be carefully monitored during treatment of hyperthyroidism.

We also suggest that you visit www.felinecrf.com. This is an excellent website with extensive information on chronic renal failure in cats in a written format that is easy to read and understand.



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