Chronic renal failure, sometimes referred to as kidney disease, is a serious disease that progresses over time, and is one of the most common conditions affecting cats. Chronic renal failure can occur in cats of any age but is most commonly seen in middle-aged to senior cats. Around one in five cats over 15 years of age has renal failure. In general, chronic renal failure is seen about three times more frequently in cats than it is in dogs.
Although the disease is irreversible once advanced, appropriate support and treatment can both increase the quality of life of affected cats and prolong life by slowing down the progression of the disease.
Chronic renal failure occurs when long-standing, irreversible damage to the kidneys impairs their ability to filter and remove waste products from the blood. In most cases, the exact cause of the disease remains unknown. Biopsies taken from affected kidneys will often show large amounts of fibrous tissue has replaced the normal kidney tissue, often with some inflammation — ‘chronic interstitial nephritis.’ However, these fibrous changes are also present in a number of diseases. There are, however, some well-recognised causes of chronic renal failure,including:
Polycystic kidney disease, an inherited condition seen mainly in Persian and Exotic cats where normal kidney tissue is gradually replaced by multiple fluid filled cysts that develop within the kidneys.
Kidney tumours such as lymphoma, a solid tumour of white blood cells, can affect the kidneys and cause renal failure.
Bacterial infections of the kidneys — ‘pyelonephritis’ — may occur as an extension of bladder infections, and sufficiently damage the kidneys to cause renal failure.
Damage to the kidneys by toxins, defects in the development of the kidneys at birth, persistent inflammation such as glomerulonephritis are also known causes.
In most cases a specific cause cannot be found for renal failure, but where an underlying cause can be diagnosed, and is treatable, there may be some potential to halt progression of the disease.
The onset of chronic renal failure is slow and insidious, although occasionally signs may appear to develop quite suddenly. Many of the clinical signs are quite vague and non-specific.
The most common signs seen in affected cats are a poor appetite, weight loss, dehydration, lethargy and depression. An increased thirst often goes along with increased volumes of urine being produced due to an inability to concentrate the urine in many affected cats.
Other signs may include a poor coat, vomiting, bad-smelling breath, mouth ulceration, and weakness. These signs tend to get worse over time.
Given the diverse functions of the kidneys, a wide variety of complications can arise in affected cats. These might include electrolyte abnormalities, high phosphate concentrations, acidosis (the retention of too much acid by the body), the development of hypertension and anaemia.
How is renal failure diagnosed?
Our diagnosis of chronic renal failure is made by analysis of blood and urine samples. Two substances in the blood — urea and creatinine, products of metabolism that are normally excreted by the kidneys — are commonly analysed. A urine sample is usually analysed at the same time. Typically with chronic renal failure, as well as appropriate clinical signs and increased urea and creatinine concentrations we will also see poorly concentrated urine, so urine ‘specific gravity’ is measured to assess its concentration.
If a specific cause for the renal failure, such as bacterial infection of the kidneys, can be identified then treatment for the cause may be possible. In most cases however, a cause cannot be identified and treatment is aimed at managing the renal failure.
Some cats may require initial intravenous fluids to correct dehydration, and perhaps electrolyte abnormalities, but once stable, treatment is aimed at supporting renal function and minimising the complications.
Optimal management of renal failure usually requires repeat investigations at regular intervals to identify treatable complications as they arise, e.g., anaemia, low potassium, high phosphate, urinary infections, and hypertension. Chronic renal failure is irreversible and, in most cases, will progress over time despite appropriate therapy.
Good Dietary management is important for cats with chronic renal failure, for three reasons.
Water intake: Cats with chronic renal failure are more likely to become dehydrated because of the reduced ability of the kidneys to conserve water by concentrating urine. Maintaining a good fluid intake is therefore very important. As cats generally gain much of their water from their food, whenever possible, cats with chronic renal failure should be fed canned (or sachet) foods rather than dry foods.
Protein content: A cat with renal failure should have a low protein diet. Many of the toxic products that accumulate in the blood in renal failure are due to protein breakdown; feeding a low protein diet will minimise this. However, too little protein in the diet can lead to excessive and detrimental weight loss. It’s best to use specially designed commercial products.
Low phosphate content: Restricting the phosphate intake appears to be quite beneficial in protecting the kidneys from further damage. Commercial diets designed to help manage renal failure are restricted in both protein and phosphate. If a cat is not eating a low phosphate/low protein diet, or if blood phosphate concentrations are high despite a low phosphate diet, ‘phosphate binders’ can be added to the diet (under veterinary supervision) to reduce the amount of phosphate absorbed.
Commercial diets for cats with renal failure also often have additional fibre and polyunsaturated fatty acids, which may offer some additional benefits in the management of the condition.
Cats with chronic renal failure tend to become dehydrated, with significant adverse effects on kidney function. A good supply of water should always available, and cats should be encouraged to drink by offering water from different bowls, offering flavoured waters (chicken or tuna, for example), etc. In some patients, usually those with advanced renal failure, there may be some benefit from intermittent administration of fluids by intravenous drip, during visits to the hospital.
Other treatments are generally aimed at specific complications that can arise as a result of renal failure, including:
Potassium supplementation to help combat low blood potassium levels.
Cats with chronic renal failure that also develop hypertension are at risk of developing further problems (such as bleeding into their eyes and retinal detachment leading to blindness, or bleeding into the brain causing neurological signs) in addition to the high blood pressure potentially further damaging the kidneys. It is important to treat hypertension when it is diagnosed, usually with medication.
In advanced renal failure, anaemia is common and can contribute to lethargy and weakness. Depending on the cause and severity treatment options include anabolic steroids, iron supplementation, management of any gastrointestinal ulcers and, in some advanced cases supplementation, with erythropoietin — the hormone that stimulates red cell production.