Chronic renal failure (CRF) in cats is a progressive disease caused by long-term insult to the kidneys which, over time, damages their ability to concentrate urine and remove nitrogenous waste products from circulation. CRF is one of the most common causes of death in companion cats. Unfortunately, the symptoms of chronic renal failure usually are not apparent until the cat's kidneys have already been severely and irreparably damaged. By the time CRF is diagnosed, roughly 70% of functional renal tissue already has been destroyed.
Causes of Feline Chronic Renal Failure
Why cats develop chronic renal failure is not well-understood. It may be that with advancing age, the kidneys simply wear out. Genetics appear to be a factor as well, with a predisposition for familial inheritance reported in certain breeds. Other contributing factors include:
Exposure to poisons (nephrotoxins are substances that destroy kidney cells)
Congenital kidney disorders (those existing at birth)
Prior episodes of acute renal failure
Chronic urinary tract obstruction (narrow urethra, chronic infection, kidney or bladder stones)
Drugs (especially nonsteroidal anti-inflammatory drugs [NSAIDs] and certain nephrotoxic antibiotics)
Polycystic kidney disease (a common congenital defect of the kidneys)
Lymphoma (a specific type of cancer)
Infectious diseases (especially feline leukemia virus and feline infectious peritonitis)
Exposure to heavy metals (mercury, lead, thallium)
Possibly diabetes mellitus
Abdominal trauma (especially when the pelvis is fractured and the bladder is ruptured)
A number of other, kidney-specific diseases can contribute to chronic renal failure, such as glomerulonephritis, pyelonephritis, tubulonephrosis, amyloidosis and tubulointerstitial nephritis. A veterinarian is the best person to discuss these specific disorders with the owners of affected cats.
Unfortunately, the cause of chronic renal failure in cats usually is never determined. Regardless of the specific cause, CRF ultimately is the end result of serious insult to kidney cells over along period of time. Once approximately 70% of functional kidney tissue has been damaged, the affected kidney can no longer concentrate urine and remove waste products from the blood. As waste products build up in circulation, they cause a number of medical consequences. Chronic renal failure is progressive and irreversible.
Prevention of Chronic Renal Failure in Cats
Because veterinarians often cannot determine the cause of chronic renal failure, owners may struggle with the thought that maybe they could have done something to prevent their cat's disease. They should not engage in that futile exercise. The majority of chronic renal failure cases cannot be prevented, and most of them are not particularly responsive to treatment. At this time, many feline CRF cases can be managed, but none can be cured. Companion cats – especially those over 7 years of age -- should receive an annual veterinary examination with blood and urine screening to monitor kidney function and the health of other vital organs. Dietary management can be helpful; a number of good commercial renal diets are available with a veterinary prescription. Of course, free access to fresh water is always important. Cats with known familial renal disease should not be part of a breeding program.
Cats with chronic renal failure can be asymptomatic for months to years. Early diagnosis of CRF and conscientious supportive care can delay progression of the disease and help maintain the cat's quality of life.
Chronic renal failure (CRF is caused by long-term insult to the kidneys. CRF can be present without overt clinical signs; this stage of the disease is called renal insufficiency, rather than renal failure. Unfortunately, once sustained clinical signs appear, the kidneys have lost most of their ability to filter waste products from circulating blood, excrete the end-products of metabolism in the urine, regulate blood pressure, contribute to red blood cell production and regulate the concentrations of hydrogen, sodium, potassium, phosphate and other electrolytes in the cat's system.
Symptoms of Feline Chronic Renal Failure
When the symptoms of CRF do become noticeable, they typically include one or more of the following:
Marked increase in thirst and water intake (polydypsia)
Marked increase in urine output (polyuria)
Urination in inappropriate places (outside the litter box)
Urination at inappropriate times (during sleep)
Decreased or even complete absence of urination (anuria)
Hunched body stance (due to abdominal pain)
Bloody urine (hematuria)
Loss of appetite (inappetance; anorexia; likely due to nausea)
Bad breath (halitosis; uremic breath odor – smells like ammonia)
Drooling/excess salivation (ptyalism)
Brownish discoloration of the surface of the tongue
Poor hair coat (dry; flaky)
Decreased self-grooming activities
Poor body condition
Pale gums and other mucous membranes
Altered cognition (changes in mental state)
Elevated blood pressure (hypertension)
Blindness (sudden onset)
Cats at Increased Risk
Chronic renal failure is more common in cats than in dogs. Certain breeds seem to be predisposed to developing CRF. These include the Maine Coon, Abyssinian, Persian, Siamese, Russian Blue and Burmese. Elderly cats usually develop some degree of renal failure, depending upon how long they live. Hyperthyroidism and chronic renal failure are often seen in the same aging cat, as both are considered to be geriatric feline diseases. Cats with prior episodes of acute renal failure have an increased risk of developing chronic renal failure.
Most cats suffering from symptomatic chronic renal failure (CRF) are severely ill. Early diagnosis and treatment may help to delay further kidney damage.
Diagnosis of Feline Chronic Renal Failure
A number of techniques are available to diagnose chronic renal failure in cats. Routine blood evaluations can detect evidence of CRF at an early stage. Most veterinarians recommend that these tests be performed annually on cats at and after 7 years of age. Blood chemistry profiles will identify the levels of circulating waste products, including blood urea nitrogen (BUN), phosphorus and creatinine, which normally are eliminated in the urine by well-functioning kidneys.
Consistently elevated levels of these substances in blood reflect declining kidney function. Anemia, which is commonly associated with chronic renal failure, can also be shown by routine blood work (a complete blood count, or CBC). A full blood panel can also help identify or eliminate other causes of the cat's clinical signs, such as diabetes or hyperthyroidism.
A urinalysis is a simple diagnostic tool that can provide a great deal of information about a cat's kidney function and overall health. The results of a urinalysis can identify a urinary tract infection and can also measure the concentration of the cat's urine. Cats in chronic renal failure usually drink large amounts of water and urinate frequently, because their body is trying to flush excess waste products out of circulation. Reduced kidney function affects the kidneys' ability to concentrate urine. As a result, very dilute urine is a common sign of chronic renal failure.
A thyroid panel (run on a blood sample) is often recommended in aging cats to rule out hyperthyroidism. Hyperthyroidism may exist apart from or in conjunction with renal failure, and if it is present the treatment options may change. Because many cats with CRF have high blood pressure (hypertension), their blood pressure is usually routinely monitored.
When chronic renal failure is suspected, the veterinarian may recommend an abdominal ultrasound to obtain an in-depth look at the cat's kidneys. This procedure is painless and non-invasive, and the results can provide a great deal of critical information about the kidneys' functional status. Ultrasonography also may disclose other related or unrelated abdominal abnormalities. Abdominal radiographs (X-rays), with or without use of injectable dye, can show abnormally small or enlarged kidneys, which often are associated with CRF. These procedures may also provide information about the actual cause of the cat's disease, such as kidney or ureter stones (nephroliths, ureteroliths), tumors, cysts or other forms of physical obstruction.
Surgical biopsy of the kidneys can be used in appropriate patients to identify the extent of kidney damage. However, kidney biopsies are not routinely taken in cats. The most common use of this diagnostic tool is when the cat's kidneys are enlarged (renomegaly) or to rule out neoplasia (cancer; especially lymphoma), feline infectious peritonitis (FIP) and other conditions.
While it is important to diagnose CRF accurately, unfortunately there is no cure. Treatment options are limited to managing the symptoms and trying to delay progression of the disease.
Chronic renal failure (CRF) can exists but be asymptomatic in cats for a very long time – even for years. Normally, by the time an owner notices symptoms of renal failure and a diagnosis is made, the condition is irreversible. Nevertheless, there are a number of supportive and management techniques that can help maintain the cat's quality of life. The goals of treating feline renal failure are to alleviate the signs of uremia (which is the nitrogenous waste build-up in circulation), delay progression of the disease and make the cat as comfortable as possible, for as long as possible.
Treatment Options for Cats with Chronic Renal Failure
The most effective initial treatment for cats in chronic renal failure is aggressive fluid therapy to address dehydration, anorexia and vomiting. Because the cat's kidneys are unable to fully perform their normal tasks, circulating waste products must be flushed out of circulation as frequently as possible. Over-hydration of the animal helps accomplish this. Fluid therapy is typically administered intravenously at first, which is an inpatient procedure. Once the cat is sufficiently rehydrated, fluids can be given by a subcutaneous route. Subcutaneous fluids are injected under the skin, normally in the scruff of the cat's neck between the shoulder blades. How frequently fluids are administered depends upon the extent of kidney damage (or, conversely, the extent of functional kidney tissue). Fortunately, most cat owners are able to administer subcutaneous fluids at home without difficulty, after brief instruction from their veterinarian.
Additional supportive care is important to manage cats with chronic renal failure. A strict "renal diet," commercially available now from several cat food manufacturers, will almost always be recommended by the veterinarian. Renal diets are typically low in protein, sodium and phosphorus. They are designed to reduce the amount of circulating metabolic waste products, in order to reduce stress on the cat's kidneys. The protein source should be of particularly high quality. Affected cats need adequate caloric intake to prevent weight loss. In fact, it usually is more important for a cat with CRF to maintain an appropriate body weight than it is to eat a diet with some special nutritional composition. Appetite stimulants may be necessary, because many cats do not tolerate dietary changes well, and they seem to find renal diets particularly unpalatable. Canned food may be a better option than dry food for cats with chronic renal failure, because of the greater water content. Cats with CRF should have unlimited access to fresh water at all times.
Oral or injectable medications are available to help control high blood pressure, address anemia and limit protein loss in the urine – all things that are beneficial to cats in chronic renal failure. If a cat is vomiting or has gastric (stomach) ulceration, the attending veterinarian can recommend a variety of over-the-counter and prescription medications to decrease gastric acidity and soothe the stomach lining. Vitamin and mineral supplementation may be recommended, including vitamin B, sodium bicarbonate, potassium gluconate, potassium citrate, vitamin D or calcitriol supplements, among others.
Blood transfusions may be necessary in cats with severe renal-related anemia. Human recombinant erythropoietin is available for use in cats to counteract anemia, as well.
Kidney transplants have become a legitimate option for owners of some cats with chronic renal failure. Survival after surgery is reportedly between 70% and 85%, with some cats living years post-operatively. Medication must be given long-term after a kidney transplant to try and prevent rejection of the donor organ. These drugs have a number of potential side effects, and their administration must be carefully managed. Kidney transplantation is only offered at a few veterinary teaching hospitals and specialty referral centers. The costs associated with the surgery typically exceed $5,000. However, transplantation is something for owners to discuss with their veterinarian if they are interested, particularly if their cat is only mildly to moderately ill and does not have underlying systemic illness. The most common method for identifying donors is to test shelter cats for compatibility. When a match is found, the shelter animal donates one kidney to the cat with CRF. The owner of that cat adopts the donor cat and agrees to provide it with a loving home for the rest of its life.
Regardless of the particular treatment protocol, cats with CRF should be monitored by their veterinarian on a regular basis to follow the progression of their disease.
The prognosis for cats with chronic renal failure is difficult to predict and depends upon a number of different factors, including how severely the kidneys have been damaged and the amount of normally functioning kidney tissue. Since this disease is incurable and progressive, the focus of management is on maintaining the best quality of life for the animal for as long as possible. Many cats diagnosed with CRF have happy months or even years of quality life ahead of them, if they are managed appropriately. Unfortunately, chronic renal failure is almost always ultimately fatal. The owner should have an honest discussion with their veterinarian about which treatment options are realistically available, and how to know when it is time to let the cat go peacefully.