Renal (Kidney) failure is the inability of the kidneys to remove waste products from the blood. The buildup of toxic wastes produces the signs and symptoms of uremic poisoning. Kidney failure can come on acutely or occur gradually over weeks or months. Chronic renal failure is a leading cause of death in pet cats.
Causes of acute kidney failure include the following:
Causes of chronic kidney failure include these:
Chronic renal failure and hyperthyroidism seem to often go hand in hand, since they are both geriatric diseases. Treatment of hyperthyroidism may unmask underlying chronic renal failure.
Cats with kidney diseases do not begin to show signs of uremia until about 70 percent of their nephrons are destroyed. Thus, a considerable amount of damage occurs before any signs are noted. The degree of renal failure can be determined by looking at laboratory data and tracking the progression of certain parameters.
One of the first signs of kidney failure is an increase in the frequency of voiding. Because the cat is voiding frequently, it might be assumed that her kidneys are functioning properly. Actually, the kidneys are no longer able to conserve water efficiently. Cats will go to the litter box several times a day and may also begin to urinate outside the box, since the box is getting dirty faster. This large urine output must be compensated for by increased fluid intake, and the cat will drink a lot more than usual. Also, because the urine is dilute (not concentrated), bacterial infections of the bladder and kidneys are much more common.
As renal function continues to deteriorate, the cat begins to retain ammonia, nitrogen, acids, and other waste products in the bloodstream and tissues (uremic poisoning). Blood chemistries will determine the exact levels of these metabolic products. Cats in the later stages of kidney failure may produce less urine than normal and, eventually, no urine at all, which leads to rapid decline.
Signs of uremia include apathy and sluggishness, loss of appetite and weight, dry haircoat, a brownish discoloration to the surface of the tongue, and ulcers on the gums and tongue. The breath may have an ammonia-like odor. Vomiting, diarrhea, anemia, and episodes of gastrointestinal bleeding can occur. Eventually, the cat falls into a coma and dies.
Diagnosing kidney failure may require a number of techniques. X-rays, with or without dye studies, along with ultrasound evaluations, can be important. Blood work, especially blood chemistry panels that look for toxic waste levels in the blood, should be done. Many cats will show increased levels of BUN (blood urea nitrogen), creatinine, and phosphorus. Anemia will show up in cats with chronic renal failure.
A urinalysis will show if the kidneys can still filter and concentrate the urine. Looking at urine sediment may suggest a cause for the kidney failure. ERD-HealthScreen is an early detection test that looks for the protein albumin in the urine (microalbuminuria). It is hoped that with early detection and treatment, the progression of kidney failure can be slowed. However, many inflammatory conditions, such as gingivitis, may also cause microalbuminuria.
Acute kidney failure can be reversed if the underlying cause can be corrected before it permanently damages the nephrons. If the insult is severe, hemodialysis (more commonly called dialysis) may be necessary to try to give the kidneys a chance to heal. Dialysis is most commonly used short term to treat acute renal failure or toxicities, or while a search is conducted for a transplant candidate. Dialysis is extremely expensive, can only be done at a few veterinary referral centers, and still requires extensive medical management of the cat in addition to the dialysis sessions.
Most cases of chronic kidney failure occur in cats who have sustained irreversible damage to the kidneys. However, these cats may still have many happy months or years of life ahead, with proper treatment. It is extremely important to be sure these cats take in enough water to compensate for their large urine output. A supply of fresh, clean water should be available at all times. Many cats will need supplemental fluids, given either intravenously at the veterinary hospital or subcutaneously at home.
The diet of a uremic cat should include protein of high quality, but lower in total amount, to minimize the amount of phosphorus and nitrogen that must be excreted by the kidneys. Special diets are available through your veterinarian. Canned foods are better than dry foods, because the canned food adds fluid to the diet. Prescription diets that are used for cats with kidney failure include Eukanuba MultiStage Renal, Purina Veterinary NF, Hill’s Science Diet k/d, Royal Canin Modified Formula, and Royal Canin Renal LP 21. Your veterinarian can also guide you to appropriate homemade diets.
Phosphorous restriction in the diet is important, although phosphate binders, such as aluminum hydroxide salt (Amphogel) can also be given. Vetoquinol has produced a veterinary product called Epakitin that is a palatable powder that also binds phosphates. However, this product also contains calcium, which may be contraindicated in the later stages of renal failure. Large amounts of B vitamins are lost in the urine of uremic cats. These losses should be replaced by giving vitamin B supplements. Sodium bicarbonate tablets may be indicated to correct an acid-base imbalance. Potassium may also need to be supplemented. The kidneys are also important in the production of vitamin D. Cats in chronic renal failure may benefit from the addition of calcitriol to their therapeutic regimen. Your veterinarian may need to order special compounded versions of calcitriol to get the appropriate dosage for a cat.
Vomiting may need to be controlled with medications such as famotidine, ranitidine, omeprazole, or others, until the renal condition is stabilized.
Erythropoietin may be used to help counteract the anemia associated with long-term renal failure. Currently, human recombinant erythropoietin is used, which may lead to immune-based destruction of red blood cells and a renewal of the anemia over time. Research is continuing for a safe feline alternative.
Cats with hypertension will need therapy to lower their blood pressure.
A uremic cat who becomes ill, dehydrated, or fails to drink enough water may suddenly decompensate; this is known as a uremic crisis. The cat should be hospitalized and rehydrated with appropriate intravenous fluids and balanced electrolyte solutions.
Some exercise is good for a uremic cat, but stressful activity should be avoided.
Another option to consider for cats with terminal kidney failure is a kidney transplant. Kidney transplants are only done at a few veterinary referral centers but are becoming more common. As with human transplant patients, drugs must be given post-transplant to prevent rejection problems. These drugs are quite expensive and must be carefully calibrated to minimize side effects. Also, it was recently reported that cats are at a higher risk for developing diabetes due to the use of these drugs.
The current method for finding kidney donors is to test shelter cats for tissue compatibility. The shelter cat then donates one kidney-cats, like people, can do fine with just one healthy kidney. The shelter cat is then adopted by the family of the recipient cat, who must agree ahead of time to provide a home for the donor cat for the rest of her life.