What is CRF?

Description of CRF (also called CRI, Chronic Renal Insufficiency)

Approximately 200,000 tiny structures (nephrons) in the kidneys eliminate waste products and regulate electrolytes in the body. CRF results when these nephrons begin to die off and waste products and electrolytes can no longer be processed effectively. The waste then accumulates in the cat's body. In effect, a cat in CRF is being poisoned by the waste that the kidneys are unable to filter. Electrolyte imbalances, anemia and blood pressure problems may also occur as the kidneys continue to deteriorate.

The Kidneys

The kidneys have five primary functions:

• Filtering waste products from the body (primarily urea and creatinine).
• Regulating electrolytes (potassium, calcium, phosphorus and sodium).
• The production of erythropoietin, which helps to stimulate the bone marrow to produce red blood cells.
• The production of renin, an enzyme that controls blood pressure.
• Production and concentration of urine

Symptoms of CRF

CRF can only be accurately diagnosed with clinical tests. There are some symptoms and behaviors that indicate the likelihood of CRF and, if these are observed, the cat should be tested as soon as possible. The most telling signs are increased thirst (polydipsia) and excessive urination (polyuria). As the condition progresses, your cat may experience loss of appetite, nausea and vomiting, weight loss, poor hair coat and emaciation. Only 30% of kidney capacity is needed for normal functioning. Therefore, no symptoms will be seen until approximately 70% of renal function is lost. It is important to begin treatment as soon as the first symptoms appear. Even with diet control, drugs and fluid therapy, you will eventually see at least some of the symptoms on the following list. Not all cats will exhibit all symptoms. Excessive urination Increased thirst Nausea and gagging Licking lips Grinding or cracking sound in jaw Vomiting (both clear/foamy liquid and food) Drooling Dehydration Hunching over the water bowl Stomach irritation (uremic gastritis) Constipation Loss of appetite Weight loss Muscle wasting Emaciation Poor hair coat Halitosis (ammonia smell) Lethargy Sensitivity to sound Eating litter Weakness Depression Oral ulcers Detached retinae Convulsion, low temperature, coma (end-stage)

Chronic vs. Acute Renal Failure

Renal failure may be either chronic or acute. Chronic Renal Failure (CRF) is a progressive, irreversible deterioration of kidney function. Because cats hide their illnesses and the very early signs of CRF are subtle, this disease may only be recognized when the patient reaches the 70% deterioration level and more dramatic symptoms are observable. The seemingly sudden onset may appear to be an acute condition but is most often a crisis point of CRF. By comparison, Acute Renal Failure (ARF) is characterized by an abrupt shutdown of kidney function, most often accompanied by oliguria (reduced urine production). The primary causes of ARF in cats are: urinary obstructions, infectious diseases, trauma, and the ingestion of toxins - the most common one being ethylene glycol which is contained in antifreeze. ARF is extremely serious and can quickly become fatal. Immediate veterinary treatment is imperative. Though the prognosis is usually poor, if damage has not been too severe and medical treatment is aggressive, it may be possible for normal kidney function to be restored. For additional information about feline ARF, we recommend this website:
Acute Renal Failure

Age-related Deterioration

CRF is one of the leading causes of illness and death in older cats. If your cat is age seven or older, it's a good idea to check for CRF during each annual exam, with a blood test, urinalysis and blood pressure measurement. With early detection, proper diet, and hydration, cats may remain happy and active for quite some time before the inevitable decline. See the Tests and Diagnostics section for more information on identifying CRF.

What Causes CRF?

CRF may have one or more causes. The common contributing factors are age, genetics, environment, and disease. In recent years, more attention has been directed towards high blood pressure, low potassium levels, acidified diets, and dental disease as possible contributors to the development of CRF. Research has indicated that some breeds have a higher rate of CRF than others. The Maine Coon, Abyssinian, Siamese, Russian Blue, Burmese, and Balinese appear to be more likely to develop CRF than other breeds. Although CRF can occur at any age, it is usually a disease of older cats. With dietary improvements in cat food, advances in feline medical care and more cats living indoors, cats are now living much longer and their bodies eventually wear out just as human bodies do.

Many renal diseases result in CRF. Usually the diagnosis in the vet’s office is simply CRF because the cause cannot be determined in most cases. Causes can, however, be divided into two groups – congenital and acquired. Congenital kidney disease may progress and turn into CRF in kittens and younger cats. We have listed some of the diseases and conditions that can cause CRF below with a very brief description. For additional information, see our Links Page under the section titled Other Kidney Disease Links.

Congenital kidney diseases:

Acquired kidney diseases:

Because there is no single, overwhelming cause of CRF, there is no definitive protocol for CRF prevention at this time. Not all cats will develop CRF. Statistical studies give hints about what may be helpful. However, since there are several possible mechanisms that may cause the onset of CRF, attempts at prevention may not be efficacious.

Contributing Factors

Acidified Diet There is speculation that acidified diets, commonly fed to cats with lower urinary tract disease, may reduce absorption of potassium and thus contribute to hypokalemia and either cause or aggravate metabolic acidosis. Potassium Imbalance Low potassium is a possible cause of CRF and, at the very least, may be an early warning sign. It has been suggested by some veterinarians that potassium supplementation should begin when the potassium level is on the low side of normal rather than waiting until it is below normal, the reasoning being that early potassium supplementation may delay the progress of CRF. Cats in renal failure are unable to prevent excessive potassium loss and the body will extract potassium from tissue to maintain blood levels, thereby masking the actual potassium deficiency as measured by a blood test. ALWAYS consult your vet when supplementing potassium, whether your cat is in the early, middle or end-stage of CRF. For additional information, including the dangers of both low and high potassium, see the Medications section of this site. The Dental Connection It is a good idea to have a mouth, teeth, and gum examination done during each annual examination. Just as in people, removal of tartar, teeth cleaning, etc. can be beneficial in keeping a cat healthy. The bacteria present in the mouth resulting from dental problems can certainly contribute to CRF. A significant percentage of the letters we've received from visitors to the Web site mention that CRF was diagnosed either just prior to or just after routine teeth cleaning or dental surgery. The connection between dental procedures and the diagnosis of CRF may be the result of a number of factors. The routine blood work done prior to or after dental surgery may reveal CRF that has been present in the patient for some time. The anesthesia used during oral surgery could exacerbate existing CRF and cause the sudden appearance of symptoms. Be sure to request that any anesthesia be a type that does not tax the kidneys. The oral surgery itself may endanger the kidneys by causing the release of bacteria and their toxins during the procedure. Talk to your vet about administering antibiotics for a time prior to dental work. High Blood Pressure The relationship between the kidneys and blood pressure is complex. The kidneys play a crucial role in regulating blood pressure. The kidneys are also subject to damage from high blood pressure. Further, high blood pressure, by forcing the nephrons to work at above their normal capacity, can mask CRF for a while. The increased pressure causes the nephrons to deteriorate more rapidly, thus accelerating the course of CRF. Treatment for Hyperthyroidism Hyperthyroidism is one of the most common diseases of cats, particularly middle-aged and senior cats. Hyperthyroidism increases the blood flow to the kidneys and may mask symptoms of CRF. Recent studies indicate that a significant percentage of cats who were treated for hyperthyroidism (whether the treatment was surgical, radiological, or a life-long prescription for Tapazole) showed symptoms of CRF. These treatments reduce the thyroid hormone in the cat's system. Among other things, this reduces the blood flow to the kidneys. CRF that had previously been masked becomes apparent. Sub-clinical kidney failure can become clinical and even healthy kidneys can undergo some deterioration. It is crucial to monitor kidney function on a regular basis in cats who are being treated, or who have been treated for hyperthyroidism. Links to additional information about the CRF/Hyperthyroidism connection in cats: Changes in renal function in cats following treatment of hyperthyroidism using I131 Effect of treatment of hyperthyroidism on renal function in cats Changes in renal function associated with treatment of hyperthyroidism in cats Effects of methimazole on renal function in cats with hyperthyroidism