Kidney failure in cats
Renal (kidney) failure is very common with cats - three times more so than with dogs. It is estimated that one in five cats will suffer from renal failure once over the age of 15. However, though most common in middle-aged and old cats, younger cats are not immune - the problem can strike at any age. Renal failure can be acute (ARF) or chronic (CRF). Acute Renal Failure is very dangerous. There is a rapid shutdown of kidney function which is clearly reflected in the reduction of urine production, leaving the cat unable to eliminate dangerous wastes from its body. ARF is generally the result of urinary obstruction, infection, trauma or because the cat has swallowed something poisonous. A particularly dangerous toxin in this regard is anti-freeze liquid which contains ethylene glycol. ARF is very serious and can kill a cat very quickly. Even with rapid treatment, the cat might not survive; and if it does, its life thereafter will depend on the extent of the kidney damage.
|Whilst ARF strikes quickly, Chronic Renal Failure is a slow progressive disease. In most cases where CRF is diagnosed the kidney damage is already substantial (up to 70% loss of function). Unfortunately CRF is irreversible and although appropriate support and treatment can slow down the disease, the disease will eventually progress to a complete shutdown of kidney function.|
Why is kidney failure so devastating?
In mammals the kidneys have a number of important functions. The most important of these functions are: filtering waste products from the blood, mainly through production of urea and creatinine; the production and concentration of urine to remove these wastes; regulation of the level of potassium, calcium, phosphorus and sodium; the production of an enzyme called renin which controls the blood pressure and the production of erythropoietin, which stimulates the production of red blood cells in the bone marrow.
Because of the multiple function of kidneys, kidney failure may result in a number of additional diseases including increased blood toxicity, heart problems, stroke, and anemia. Therefore the management of cats with CRF also involves the management of these additional medical conditions.
Symptoms of renal failure
Kidneys come with a lot of built-in redundancy. For a start, there are two of them, but one is fully sufficient to maintain a healthy body. In fact it has been estimated that even with 70% damage to a kidney, cats may still show no signs of illness. CRF is therefore very difficult to diagnose, and when it is finally diagnosed, the damage to the kidneys is usually already considerable. One of the major problems in accurate diagnosis of CRF is that all the symptoms seen in cats with CRF can just as easily by symptoms of a number of other diseases. An accurate diagnosis can only be done with clinical tests.
The most telling signs that a cat has CRF are increased thirst, resulting in the cat drinking excessively, and consequently urinating to the same degree. As the disease progresses the cat is likely to lose appetite, and consequently lose weight. Vomiting, drooling and constipation are also common. In the later stages the cat may become very lethargic and weak with muscular wasting. She may also show signs of depression. If your cat shows any or all of these symptoms CRF should be considered and the cat should be tested as soon as possible.
Diagnosis of renal failure
To check for CRF the vet will take urine and blood samples. Analysis will be done to check for urine concentration. Excessively dilute urine indicates that the kidneys are not processing waste material. The vet will test for the level of blood urea nitrogen and creatinine in the blood. An increased level of these substances is a certain sign of malfunctioning kidneys.
What causes renal failure?
In most cases, what has caused the Chronic Renal Failure is very difficult to pin down. However, there are some conditions which are known to induce CRF. These include:
- kidney tumours
- polycystic kidney disease, an inherited condition where normal kidney tissue is gradually replaced by fluid cysts which develop inside kidneys. This condition is mainly seen in exotic and Persian cats
- chronic inflammation, for example glomerulonephritis (an inflammation of the glomeruli, bundles of tiny vessels inside the kidneys. The damaged glomeruli cannot effectively filter waste products and excess water from the bloodstream to make urine. The kidneys appear enlarged, fatty, and congested.)
- bacterial infection which may occur as a result of bladder infections
There are also a number of other factors which can contribute to kidney damage, for example a low potassium level increases the risk of CRF, which is why the vet might prescribe potassium supplements to slow down the progress. Acidified diets may also be recommended for cats suffering from lower urinary tract disease, as this disease may reduce the absorption of potassium and so contribute to a low potassium blood level. Any bacterial infection, including dental infections may put the cat at risk of CRF.
Finally there is a statistically significant correlation between hyperphyroiditis and CRF. The effects here may be indirect. In hyperphyroiditis there is a an increased blood flow to the kidneys, which may temporarily mask the development of CRF. Following treatment, the blood flow decreases allowing for the CRF to be more apparent. So in this case the hyperphyroiditis itself is not the cause but it masks the disease, allowing it to get worse for longer without being detected.
Management of chronic renal failure.
Not all CRF cases are fatal. For example, when the renal failure results from a bacterial infection of the kidney which is quickly identified and successfully treated, if the damage to the kidney is not substantial, the cat will recover. However, in most cases the cause is unknown and treatment focuses on minimizing the symptoms and encouraging whatever function the kidney still has. The optimal management of CRF requires checks at regular intervals for any complications arising from the CRF, such as urinary infection, electrolyte imbalance (low potassium, high phosphate levels), anaemia, high blood pressure and so on. These conditions can be treated, thus making the complications arising from the disease less dangerous.
One problem associated with CRF is chronic dehydration. Some cats may initially require intravenous fluids to stabilize the problem. Thereafter the liquid intake can be managed by diet. It is recommended that the cats are with CRF should be switched from dry to canned food to increase their liquid intake. It is also essential that a good supply of fresh water is always available. (Note that in some areas cats are put off drinking tap water by the chemicals added by the water company.)
ACE-inhibitors, eg, benazepril, are a class of drugs that act predominantly as vasodilators (i.e. they dilate blood vessels). In humans with renal failure these drugs are commonly used to help manage the disease, as they appear to be beneficial to renal function and reduce protein loss through the kidneys (which can be elevated and can be harmful in renal failure).
There is some evidence that these drugs may benefit cats with renal failure too, but it is not certain whether this applies to all cats. Current knowledge suggests that perhaps cats which lose a lot of protein in their urine are most likely to benefit. With all cats where this type of drug is used, it is sensible to monitor blood and urine results as well as clinical signs to to see if the medication is helping.
In the mid-1980s, the School of Veterinary Medicine at the University of California, Davis (UCD) pioneered a kidney transplant program in the hopes of making this option readily available to caregivers with CRF cats. The surgical procedure and postoperative protocol have been perfected and transplantation is no longer considered experimental. Renal transplants are available now in many veterinary hospitals. Feline renal transplantation is now an accepted and relatively safe treatment for patients in renal failure. A successful transplant (the success rate is now 80 to 90 percent) allows the cats to return to normal activity. Cats surviving their first year after the operation may go on to live for many years. The survival rate depends on the age and the overall health of the cats, since cats with renal failure are frequently around 15 years old. An extended life expectancy of 2 to six or more years is common. Indeed the longest surviving feline patients at present had their transplants about 10 years ago.
Of course one of the big inhibitory factors for a transplant is the cost. This ranges from $9,000 to $11,000 and that is just for surgery itself. Then there may be additional drugs or dialysis required before or after the operation.
Note: This information is for guidance only. It is not intended to replace consultation with a licensed practitioner.