About 25 percent of the blood that courses through the circulatory system with each heartbeat travels directly to the kidneys. Given the relentless and crucially important burden that these organs bear, their well-being is essential to your cats health.
Unfortunately, feline kidneys – like their human counterparts – are susceptible to a wide range of life-threatening disorders. Indeed, says David Polzin, DVM, PhD, kidney (renal) disease is a major cause of feline dysfunction and death. Especially among older cats – those seven years of age and older – it is definitely one of the top two or three causes of morbidity and mortality, notes Dr. Polzin, a professor of veterinary medicine at the University of Minnesota Department of Small Animal Clinical Sciences.
When the kidneys and their filtering system malfunction, potentially toxic wastes start to accumulate in the recirculating bloodstream. If proper balances of water, minerals, and electrolytes (such as sodium and potassium) are not maintained, serious complications may affect other organs.
A high risk for kidney disease can be inherited, and some veterinary experts contend that long-haired breeds such as Persians and related breeds are more genetically predisposed to certain forms of kidney disease than are short-haired breeds. But the great majority of cases are acquired, and they fall into two broad categories: acute renal failure and chronic renal failure.
The essential difference between the two, according to Dr. Polzin, is that acute renal failure is a severe condition of recent onset that has become apparent within the past week or month, while chronic renal failure is a longstanding disease that has probably been there for several months or even years.
Acute Renal Failure
Common causes of acute renal failure include blockages that interfere with the flow of blood to the kidney or the flow of urine from it. Most common of all causes, however, is ingestion of substances that are toxic to the kidneys, like antifreeze, pesticides, cleaning fluids, and some feline and human medications. If a kitten eats a single ibuprofen or other anti-inflammatory drug, says Dr. Polzin, that can be enough to throw it into acute renal failure.
He notes, however, that cats of all ages are at risk. Kittens may be more likely to get into things they shouldnt, he says. But older cats, due to the nature of aging, are also susceptible.
If diagnosed at an early stage and treated promptly, kidney damage resulting from acute renal failure is potentially reversible. Indeed, when treatment is instituted early, the prognosis for full recovery may be guarded to excellent, and a rescued cat can often go on to enjoy a normal life span.
Chronic Renal Failure
Sadly, the same cannot be said for chronic renal failure, which is an incurable condition that mainly afflicts middle-aged and older cats. It occurs when 75 percent or more of functional kidney tissue – that which contains the nephrons – has been destroyed and replaced by scar tissue. Unlike acute renal failure, the onset and progression of this condition (called interstitial nephritis) is gradual, extending over many months or years.
According to Dr. Polzin, chronic renal failure is usually an idiopathic condition. That is, the exact causes are unknown, although the debilitating loss of healthy kidney tissue may be a natural endpoint for several readily recognizable conditions, ranging from a variety of kidney infections, inflammations and obstructions, to dermatitis and advanced dental disease.
By the time a cat is showing signs of chronic renal failure, the underlying cause is for the most part irrelevant, since the loss of healthy kidney tissue will preclude effective treatment of that cause. In some cases, little can be done to prolong the life of a cat diagnosed with late-stage chronic renal failure. On the other hand, Dr. Polzin observes that with proper veterinary care, it is quite common for a cat to live for one to three years following diagnosis – and in some cases, as long as six years or more.
Better Diagnostic Methods
According to Dr. Polzin, the early signs of a failing kidney include a marked increase in water consumption (polydipsia) and in urination (polyuria). The cat will also lose weight, he notes, and become more finicky about her food. Sometimes theres vomiting, but basically, the tendency to become dehydrated and drink more water are the clearest signs of a decline in kidney function. If these signs are observed, the owner should seek immediate veterinary consultation, urges Dr. Polzin.
If kidney disease is suspected, the veterinarian will perform blood tests and a urinalysis. The former will determine the blood levels of substances that would normally be shed in the urine – especially blood urea nitrogen (BUN) and creatinine. Elevated levels of these substances will indicate that the kidneys are not adequately filtering metabolic wastes. The urinalysis will provide additional information on the extent of kidney damage and whether an infection might be responsible. Further tests – involving X-rays, ultrasound, and even a kidney tissue biopsy – may be required to confirm a tentative diagnosis of renal failure.
Researchers are constantly striving to refine methods for diagnosing kidney failure. According to Dr. Polzin, the most promising recent advances have centered on improved methods of gauging kidney filtration rate by injecting certain substances and measuring their rate of disappearance from the bloodstream. These methods allow us to get extremely accurate measures of kidney function, he says, especially in cases of early-stage renal failure.
Treatment for renal failure is generally determined by the type of disorder causing it – if the disorder can be identified – and the extent of kidney damage sustained. Acute renal failure requires emergency treatment. If caused by any type of urinary tract blockage, the obstruction must be removed immediately. The use of any suspect medication must cease, and intravenous solution infusions must be administered without delay to correct fluid and electrolyte imbalances in the blood.
On the other hand, the vast majority of chronic renal failure will be addressed with what Dr. Polzin terms conservative medical management. Diet therapy is at the heart of this treatment method. The major components of the diet are reduced phosphorous, protein and salt, and sometimes increased vitamin D and omega-3 fatty acids, says Dr. Polzin.
In rare cases, surgical removal of a malfunctioning kidney may be recommended, but only if the remaining organ is strong enough to carry out both of the kidneys many tasks by itself.
Great Progress in Two Areas
In recent years, notes Dr. Polzin, significant progress has been made in two treatment areas. One is hemodialysis – a procedure that removes liquid and chemicals from the blood that the kidneys would routinely remove if they were functioning normally.
The other area of notable progress is in feline kidney transplantation techniques. Survival rates are now as high as 80 percent at some veterinary centers, and owners can expect their animals to live one to three years or longer following a kidney transplant.
He points out, however, that these sophisticated procedures are not appropriate for all ailing cats, and that they are available in only a few areas of the U.S. Transplants are costly, ranging somewhere between $5,000 and $10,000 for the procedure itself, plus the expense of immunosuppressive drug therapy for the remainder of the organ recipients life.