As owner of your pets, you must read this...
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What Healthy Feline Kidneys Do
The kidneys are essentially a filtration system for the body, not unlike those used to keep a swimming pool clean. But where a pool filter removes leaves and algae from water, the kidneys remove toxic waste products (such as urea and creatinine) which accumulate in the blood of mammals as their food is converted into energy.
However, the kidneys are not just simple filters. They're highly complex organs which also regulate blood composition and pressure.
Most notably, they control the amount of electrolytes in the blood (potassium, magnesium and calcium, which regulate heart contractions; sodium, which regulates the amount of water in the blood; phosphorous, a constituent of bones and teeth).
The kidneys also produce a substance called erythropoietin (which stimulates the bone marrow to produce red blood cells).
Finally, they produce an enzyme called renin, which maintains and controls blood pressure.
Any failure of the kidneys has a knock on effect on every other organ in the body, making them every bit as important to your cats wellbeing as, say, their heart or lungs.
However, where heart or lung failure tends to have more immediately noticeable effects, the kidneys have a considerable amount of overcapacity. You probably know that most people can survive with only one kidney. In fact, it is not until 75% of kidney function has been lost through disease that outward clinical symptoms start to be seen.
Diseases That Cause Kidney Failure In Cats
Kidney failure is commonly caused by one of a number of diseases, categorised by experts according to whether they are acquired or congenital.
Acquired Kidney Diseases
Kidney diseases that the cat acquires during the course of its lifetime, usually as a result of normal wear and tear, infection or injury.
Congenital Kidney Diseases
Kidney problems that the cat has had from birth. They may or may not have been genetically inherited from the cat's parents.
Whether acquired or congenital, kidney failure is also described as either chronic or acute.
Chronic Kidney Failure
Chronic kidney failure, otherwise known as Chronic Renal Failure (CRF) or Chronic Renal Insufficiency (CRI), is a progressive deterioration of kidney function over a relatively long period of time (typically months to years). As already noted, a cat may lose up to 75% of kidney function before symptoms become noticeable, at which time the cat may appear to have become quite suddenly ill.
Acute Kidney Failure
Acute kidney failure, otherwise known as Acute Renal Failure (ARF) is the sudden shutdown of kidney function, most often as a result of a urinary obstruction, an infectious disease, physical injury or poisoning. Immediate and aggressive veterinary treatment is required for cats suffering from ARF, and in some cases this will successfully reverse the disease. Unfortunately, the outlook is often poor and many cats with ARF will not survive or will be left with residual renal insufficiency.
Acquired Diseases That Cause Kidney Failure In Cats
Acquired kidney diseases are the cause of most cases of kidney failure in cats, and tend to manifest in middle to old age.
Some of the more common diseases are listed below.
Chronic tubulo-interstitial nephritis is the most commonly identified problem in cats suffering from CRF. It is often the end-stage of many causes of kidney disease, where damaged nephrons (the functional unit of kidney tissue) are replaced with fibrous tissue. Typically affected kidneys will be small and scarred.
Glomerulonephritis is a disease in which the glomeruli (which help filter urine from the blood), are damaged by inflammation.
Pyelonephritis is the name for a bacterial infection of the kidneys.
Amyloidosis is a disorder by which insoluble protein fibres are deposited in various organs of the body. When it occurs in the kidneys, their function is impaired and chronic renal failure can result. Amyloidosis can be seen as an inherited condition in Abyssinian cats.
Hydronephrosis is an excessive accumulation of urine in the kidney caused by an obstruction or blockage in the ureter - the tube linking the kidney to the bladder.
Renal lymphoma is a cancer of white blood cells affecting the kidney. Typically both kidneys will be very enlarged if this condition is present.
Congenital Diseases That Cause Kidney Failure In Cats
Congenital kidney diseases are those that the cat has had from birth. They may or may not have been inherited from the cat's parents.
Some of the more common congenital kidney diseases are listed below:
Polycystic Kidney Disease (PKD) is a condition in which cysts form in the kidneys, decreasing kidney function. It is most common in Persian and Exotic shorthair cats. Affected cats are born with lots of small cysts in their kidneys. As the cysts increase in size they compromise the surrounding normal kidney tissue, eventually causing kidney failure. Although this is a condition which is present from birth in affected cats, it may not be evident until later in life, depending on the number of cysts present and speed at which they are enlarging.
Renal Aplasia is when a kitten is born missing one or both kidneys.
Renal Hypoplasia is when the kidneys have a reduced number of functioning nephrons.
Renal Dysplasia is when the kidneys develop abnormally.
Amyloidosis is also listed under acquired kidney diseases, but it can be inherited in Abyssinian cats. It is a disorder by which insoluble protein fibres are deposited in various organs of the body. When it occurs in the kidneys, their function is impaired and chronic renal failure can result.
Diagnosis Of And Screening For Kidney Failure In Cats
Up to 75% of a cat's kidney function can be lost before it shows any outward signs of ill health. Inside the body, though, it's a different story. Earlier stages of kidney failure produce a change in the composition of your pet's blood and urine, which can be picked up with simple screening tests by your veterinary surgeon. That's important, because it's vital to catch the problem quickly if your cat is to stand the best chance of a longer, healthier life.
The question is, which screening and diagnostic tests should be carried out, and when?
Regular physical exam
Recommended for all cats over 7 years of age
A basic annual physical examination of your cat by a vet is simple, quick, non-invasive and can be carried out at low cost. What's more, it'll give your vet the best chance of diagnosing many other conditions early - not just kidney failure. Cats of any age will benefit from an annual healthcheck, but they become increasingly important in middle to old age, and are recommended for all cats over seven years of age.
A physical examination to check for early signs of kidney failure should ideally include:
• A weight check, as weight loss can be an early indicator of many diseases - including kidney failure.
• A general physical examination, which provides information on whether or not the cat is dehydrated, anaemic, whether the kidneys feel abnormal (e.g. enlarged due to polycystic kidney disease), or whether there are problems caused by other diseases.
• Blood pressure measurement, as high blood pressure is a common consequence of kidney failure in cats.
• An examination of the eyes to check for any damage caused by high blood pressure.
• A urine test. Cats normally produce concentrated urine (they evolved as desert-living creatures); dilute urine can be an early sign of kidney disease. Urine can be collected from your cat at home using non-absorbant litter provided by your vet. Alternatively urine can be collected via a procedure called cystocentesis (where urine is sampled using a needle inserted into the bladder).
It is also worth pointing out that even if urine and blood pressure checks reveal nothing untoward, they are still a useful exercise. They help to establish normal readings for your cat, against which your vet can compare the results of future tests.
Blood tests
Recommended when a physical exam indicates the possibility of kidney failure
Once two thirds to three quarters of renal function is lost, the kidney becomes less effective at excreting waste products produced by the body as it breaks down protein. Consequently, these waste products build up in the bloodstream, a condition known as azotaemia. In combination with the results of a urine test, vets can confirm a diagnosis of kidney failure by analysing blood for increased levels of two waste products: urea and creatinine.
Again, worth noting that azotaemia can be seen for reasons other than kidney failure. Common examples would include dehydration or analysis of a blood sample collected within a few hours of eating a meal. These need to be considered and eliminated as possible causes before a diagnosis of kidney failure is made.
Although blood tests are usually slightly more expensive than the tests carried out during a basic exam (such as urinalysis), they are nevertheless a routine and straightforward procedure. A small amount of blood is taken from the cat, and the sample usually sent to a laboratory for analysis.
Advanced Diagnostics
In some cases, further tests may need to be carried out in order to pinpoint the cause of kidney failure. They include:
• Renal Ultrasound
Ultrasound equipment is sometimes used to scan the kidney for the presence of diseases such as polycystic kidney disease. This is a relatively straightforward and non-invasive procedure. However, ultrasound equipment is not available in all practices, so the procedure may require referral to a specialist vet.
• Renal Biopsy
Biopsy of the kidney is not required in the majority of renal disease patients. Kidney biopsy is a specialist procedure and is usually performed in patients where cancer (e.g. lymphoma) or other rare causes of renal disease (e.g. glomerulonephritis, amyloidosis) are suspected. The procedure involves taking a sample of suspect tissue from the kidney whilst the animal is under a general anaesthetic, and sending it for laboratory analysis.
Management Of Kidney Failure in Cats
When caring for a cat with kidney disease, it is important to have realistic expectations about what can be achieved. Fact is, any damage to the kidneys is irreversible. However, there are a number of therapies and drugs which can improve and extend the life of a cat suffering from kidney failure, and the long term prognosis is relatively good in many cases.
The management of kidney failure is a highly complex subject, due to the wide variety of different symptoms that can affect an individual patient, each of which may require a different treatment or therapy.
On this site, we outline the main treatments and therapies in use today. However, the decision as to which treatment or combination of treatments is appropriate for your cat can only be made by a veterinary surgeon. This information is therefore provided only to help you better understand the recommendations made by your vet.
Please also note that some of the treatments explained on this site may not be specifically licensed for use in cats; for further information, please consult your vet.
Kidney Diets Explained
Special 'renal' diets are often prescribed for cats with chronic renal failure (CRF). There is now plenty of good scientific evidence to show that CRF cats eating these diets live longer (on average twice as long) as those not fed the diets. The diets should be introduced gradually to encourage acceptance by the cat. Renal diets are formulated to contain:
Restricted protein
Waste products are produced by the body as protein is converted into energy. So, by reducing the amount of protein in the diet, so the amount of waste needing to be processed by the ailing kidneys can be limited or reduced. This in turn can reduce the clinical signs associated with the build up of waste products in the body (called uraemic signs), such as vomiting, loss of appetite, anaemia and lethargy. The benefits of protein restriction in reducing these clinical signs have been supported by scientific studies performed both in cats and other species.
Whether dietary protein restriction actually has any impact on the progression of renal failure in cats is still a very controversial area. As nephrons within the kidney fail, the smaller number of remaining nephrons adapt to deal with the greater waste processing load placed on them. In some experimental studies, these adaptive changes have been demonstrated to be harmful to the remaining nephrons, and ultimately cause or contribute to the progression of CRF. In experimental models, restricting dietary protein has been shown to minimise these changes and thus slow the progression of CRF. At this stage, however, this benefit is only suggested (not proven) in humans, and there is no proof that cats would benefit in the same way.
Reduced phosphorus/phosphate
Phosphorus is an important mineral usually found in nature combined with oxygen as phosphate. Whilst an important component of cells and bone in the mammalian body, too much phosphate contributes towards hyperparathyroidism (over production of parathyroid hormone which regulates the amount of calcium and phosphorus in the body). In one scientific study looking at cats with naturally occurring renal disease, improved survival times were seen in those fed a phosphate restricted diet (Elliott et al, JSAP 2000, 41: 235 -242).
Increased potassium and vitamin B
Prescription renal diets are supplemented with potassium and water soluble vitamins (B and C vitamins) which CRF cats are vulnerable to losing in their urine. Potassium deficiency is covered in greater depth in the section: Managing potassium deficiency.
Reduced sodium
Renal diets usually have lower levels of sodium, which may help to reduce the risk of systemic hypertension (high blood pressure) from developing.
Palatability and calorie content
Increased palatability and calorie density helps CRF cats with a poor appetite to maintain a normal body weight.
Acid-base balance
Renal diets are formulated to help prevent acidosis (excess blood acidity - a common consequence of kidney disease) from developing in cats with CRF.
Additional dietary manipulations
Renal diets often have supplemented fibre which helps to reduce absorption of protein breakdown products across the bowel. Levels of fatty acids (e.g. omega 3 polyunsaturated fatty acids) are also often supplemented as this has been shown to slow the progression of renal disease in other species.
ACE Inhibitors Explained
ACE inhibitors, or Angiotensin Converting Enzyme inhibitors, to give them their full title, were first developed for use in man after it was found that they reduce excessive amounts of protein in the urine (which is thought to be toxic to the kidneys), reduce blood pressure, and increase lifespan. One ACE inhibitor has now been licensed for use in the management of kidney failure in cats.
Given that kidney failure cannot be cured, one of the most important aspects of treatment is to maintain the best quality of life for the patient.
So perhaps the most important benefit of this treatment was demonstrated in a trial where the owners of CRF cats treated with an ACE inhibitor noted an improvement in their cat's quality of life which was double that when diets alone were used. Furthermore, the survival times for cats suffering from severe kidney disease (cats losing large amounts of protein in their urine) increased by a factor of three after treatment with an ACE inhibitor.
In another study amongst healthy cats, an ACE inhibitor was shown to increase appetite and body weight - which is a potentially useful effect in cats with chronic renal failure (Witte et al. 2003).
An additional benefit of ACE inhibitors is that they lower blood pressure. High blood pressure (hypertension) is found as a consequence of kidney failure in around 20% of CRF cats.
ACE inhibitors are used to treat mild hypertension but additional anti-hypertensive drugs (e.g. amlodipine) may be needed in CRF cats suffering from severe hypertension.
Fluid Therapy Explained
Cats with chronic renal failure are vulnerable to becoming dehydrated. This is partly because they may not be drinking or eating sufficient fluids but also because damaged kidneys are prone to losing excess fluids in the urine. Dehydration worsens renal function and can quickly worsen the cat's clinical condition. In some cats this is a recurrent problem, necessitating frequent visits to a veterinary surgery for additional fluids (e.g. via an intravenous drip). Encouraging fluid intake is therefore essential in cats with CRF and can be achieved in a variety of ways:
• The cat should always have free access to a fresh supply of water. Provide several bowls of water within ready access.
• If possible, offer moist rather than dry renal diets.
• Supplement the diet with flavoured water or broths. For example, liquidise a few prawns in some water and offer this as a drink to the cat. Alternatively, poach some chicken or fish in water, and offer the water to the cat.
• Do not offer salty liquids (e.g. fish in brine) as this increases the risk of high blood pressure developing.
• Avoid offering milk, as this contains large amounts of phosphate, a mineral which many CRF cats are vulnerable to accumulating in excess.
• Some cats will enjoy drinking from water fountains which can be obtained from pet shops or veterinary surgeries.
In those cats that suffer from recurrent episodes of dehydration in spite of following all of these measures, additional therapies are needed. These can involve one of the following:
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Subcutaneous fluid therapy
Fluids can be administered using a needle at home. Alternatively, a special catheter can be placed under the skin by a veterinary surgeon. Placement of the catheter requires a short anaesthetic and small surgical incision. The catheter has a 'port' on the outside of the skin which is attached to a fluid-giving system. Depending on the cat's requirements, between 50 and 150 ml of fluid is given on a daily to twice-weekly basis. Medications (such as potassium) can be added to the fluids if needed.
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Fluid administration via a feeding tube
In those cats that need a feeding tube to provide their nutrition, fluids can also be given in this way.
Home fluid therapy (subcutaneous or via a feeding tube) must only be performed under the specific recommendation of a veterinary surgeon and is not needed in all CRF cases. In those cats that do not require this therapy it can be damaging to give additional fluids (placing a greater burden on the kidneys), and there is a risk of electrolyte problems if treated cats are not monitored carefully.
Other Conditions Related To Kidney Failure In Cats
Introduction
To some degree or another, kidney failure has a knock on effect on every organ in the body. However, every animal is unique, and kidney failure will affect every animal in different ways. It's impossible to predict: some will suffer very few related conditions, some will suffer them all.
In this section, we have listed some of the more common conditions suffered by cats with kidney failure, and the treatments used to control them. The list is not exhaustive, and your veterinary surgeon may recommend other therapies.
Managing poor appetite
Cats with chronic kidney failure often have a poor appetite, sometimes made worse by feeding prescription kidney diets which may be unpalatable.
General nursing techniques such as feeding warm food by hand may help. In other cases, appetite stimulants such as the anti-histamine cyproheptadine or anabolic steroids may be recommended to stimulate an adequate appetite.
In a minority of cases it may be necessary to fit a feeding tube for long-term nutritional support. Gastrostomy tubes (tubes entering the stomach directly from the outside) can be placed non-invasively via endoscopy (via the throat) or via a laparotomy (via a surgical incision in the wall of the abdomen).
Although an anaesthetic and short period of post-operative hospitalisation is required to place the tube, once in place they can be used for prolonged periods to administer blended food, liquids and medicines to the cat. Depending on the composition of the tube, it will need to be replaced after a few months (2 - 3 months for latex tubes, 6 - 12 months for silicone tubes).
Other medications should be given prior to feeding, except phosphate binders which should be given mixed with the food. Wet food, blended with water to provide a syringable consistency, is warmed to body temperature and injected into the stomach over a period of 10 - 15 minutes.
When administering food via a tube, you should be aware of signs of nausea (e.g. gulping, salivation) which indicate that the meal is being introduced too rapidly or that the stomach was not completely empty prior to feeding.
After feeding, the tube should be flushed with 5 - 10 ml of water. Initially the cat should be fed four to six times a day with equal sized meals and no meal greater than 45 ml/kg (approximate stomach capacity of the cat) in volume. Over time, it is usually possible to reduce the number of feeds a day.
The cat should always be offered food orally before feeding via the tube as appetite can vary and some cats with CRF will intermittently have a good appetite.
If the feeding tube is inadvertently removed, replacement is an urgent emergency in those cats where continued tube support is required, as the entry site heals rapidly. This will prevent easy replacement if not acted upon within a few hours. Some types of tube can be fitted through the existing gastrostomy entry site without the need for an anaesthetic in most cats, and some owners may be able to do this without veterinary assistance.
Occasionally tubes can become blocked with food or medication. Massage of the tube whilst infusing water can help to alleviate this. Coca Cola or cranberry juice can also help to break down blockages. In persistent cases, passing a catheter down the tube may be helpful and some authors advocate the use of meat tenderisers and pancreatic enzyme solutions!
Managing nausea & vomiting
Many cats with chronic renal failure (CRF) may suffer from gastritis (inflammation of the stomach lining) as a consequence of the accumulation of waste-products in the circulation. This contributes significantly to the inappetence and weight loss associated with CRF.
CRF cats may also have a build up of a hormone called gastrin, which stimulates the production of acid in the stomach, because the kidneys are unable to excrete it effectively. The resulting excess stomach acid can be controlled with low doses of H2-antagonists such as cimetidine or ranitidine.
Sucralfate may also be recommended if the cat is suffering from gastric ulceration, although it can cause constipation in some cats.
An anti-emetic drug (one that reduces nausea and vomiting), such as metoclopramide or chlorpromazine, may also be recommended to block uraemic toxin stimulation of the stomach.
Managing constipation
Constipation is not uncommon in cats with chronic renal failure, and may be exacerbated by some of the treatments (e.g. sucralfate).
Lactulose is a safe and effective treatment which has the additional benefit of trapping urea (one of the key components of urine) in the bowel, increasing its removal and helping prevent the build up of waste products in the body.
Managing potassium deficiency
Many cats with CRF will also suffer from low levels of potassium, an essential mineral which is required for many purposes including normal muscle function. Low blood potassium (hypokalaemia) results from an inadequate intake of potassium in the diet (through not eating enough) and excessive loss in the urine.
In mild cases, hypokalaemia contributes towards loss of appetite, lethargy and general weakness. In more advanced cases, the muscle weakness is severe; in some cases, the cat will be unable to hold its head up (so-called ventroflexion of the neck).
It also seems that low levels of potassium may directly affect kidney function and contribute to CRF. Potassium supplementation of hypokalaemic cats with kidney failure often results in improved renal function. By contrast, feeding a potassium-restricted acidifying diet to normal cats has been shown to actually induce renal damage.
Hypokalaemic polymyopathy is considered to be the commonest cause of generalised muscle weakness in cats and the majority of these cases are related to CRF. Routine assessment of potassium levels in the blood is therefore recommended in cats with CRF, and supplementation made where necessary.
Non-acidifying, low-protein diets help to maintain potassium concentrations, but in more severe cases, further additional potassium salts may be required. Potassium gluconate is preferable to potassium chloride which is unpalatable and may cause gastrointestinal irritation.
Although low-dose oral potassium supplementation has been advocated for all cats with CRF, a recent study showed no benefit in potassium supplementing cats with normal blood potassium levels.
Managing excessive phosphorous
Phosphorous is an important mineral usually found in nature combined with oxygen as phosphate. Around two thirds of cats with CRF have high blood phosphate levels as the kidneys are normally responsible for excreting phosphorous from the body. Whilst an important component of cells and bone in the mammalian body, too much phosphate (hyperphosphataemia) contributes towards hyperparathyroidism (over production of parathyroid hormone which regulates the amount of calcium and phosphorus in the body).
The use of low protein diets will achieve a reduced phosphorous intake, but this will not always be sufficient to prevent the hyperphosphataemia encountered in CRF. If hyperphosphataemia persists despite dietary restriction, or if the cat will not eat a prescription renal diet, then oral phosphate binders should be given with meals.
Oral phosphate binders stick to phosphate present in the diet and limit what is absorbed by the bowel. Aluminium hydroxide, aluminium carbonate or aluminium oxide have been most commonly used, however some of these compounds are no longer available. Calcium-based agents are another option (calcium carbonate and calcium acetate) but their use may lead to excess levels of calcium in the body (hypercalcaemia), so these agents should be used with care and the blood calcium levels monitored.
Managing hypertension
Systemic hypertension (high blood pressure) is a common finding in feline CRF, and although its true prevalence is difficult to determine, a recent study identified hypertension in around 20% of cats with CRF seen in a first opinion veterinary practice (Syme et al JAVMA 2002, 220: 1799-1804).
Hypertension can have serious consequences including blindness and neurological signs. Blood pressure should therefore be evaluated as a routine part of all check-ups of CRF cats and anti-hypertensive therapy prescribed to those where the average blood pressure readings, taken with the cat in a calm state, are persistently high, or where there is evidence of retinal damage (e.g. bleeding into the eye and/or retinal detachment) caused by high blood pressure.
The most commonly used drugs for treatment of feline hypertension are the calcium channel blocker amlodipine besylate and the ACE inhibitor, Fortekor. In general, amlodipine is more effective in lowering blood pressure than the ACE inhibitors although in some cats, a combination of both of these drugs may be required to achieve adequate control of blood pressure.
In humans, there is unequivocal evidence that control of systemic hypertension slows the progression of chronic renal failure. Such evidence is lacking for dogs and cats but, nevertheless, given our current state of knowledge anti-hypertensive therapy is recommended for any CRF cat with a systolic blood pressure consistently in excess of 170 - 180 mmHg or with evidence of clinical hypertension such as bleeding into the eye.
Antibiotics
Recent studies showed that a significant proportion of cats with chronic kidney failure suffer from a bacterial cystitis (infection of the urine) at some point in the course of their disease (Barber et al., 1999 ACVIM Congress). The authors found that female cats were especially vulnerable to recurrent infections.
Bacterial cystitis may cause a secondary infection: pyelonephritis (bacterial infection of the kidney), or may itself be secondary to pre-existing pyelonephritis.
It is thought that cats with CRF may be more vulnerable to the development of bacterial infections since the urine they are producing is so dilute.
In many cases, the bacterial infection does not cause signs of cystitis (e.g. squatting and straining to pass small amounts of urine frequently), which can make diagnosis of this complication difficult.
In order to make a diagnosis, your vet may ask for a urine sample from the cat, which is then assessed for microscopic evidence of bacteria in the sediment and inoculated onto bacterial culture media for growth in a laboratory.
A course of antibiotics, ideally chosen on the basis of bacterial culture and sensitivity results, is often needed for several weeks or months in order to successfully eliminate the bacterial infection.
Managing Acidosis
Metabolic acidosis is a disturbance of the acidity level of the blood. It is commonly encountered in patients with CRF and may contribute to a number of important features of CRF including vomiting, loss of appetite, lethargy, hypokalaemia (low blood potassium) and skeletal muscle demineralisation.
Treatment helps to prevent/resolve these clinical signs. Unfortunately, it is not always possible for a GP veterinarian to assess acid-base status, as expensive specialist equipment is needed for this test.
Feeding a prescription renal diet helps to prevent acidosis from developing in cats with renal disease. If the cat remains acidotic in spite of this then therapy with sodium bicarbonate, given orally, may be recommended. If the cat is receiving a urinary acidifying diet, this should be stopped and, ideally, a low-protein diet instituted. In cats with low levels of blood potassium that are also acidotic, the alkalinising agent potassium citrate may be recommended.
Managing anaemia
Progressive anaemia is common in CRF and appears to contribute to a variety of clinical signs including lethargy, inappetence, weakness and weight loss. Hormone therapy with either androgenic steroids or recombinant human erythropoietin (rHuEPO) is the most widely-used treatment for anaemia of CRF.
However, in some cats, iron deficiency can contribute to the anaemia, both through inadequate dietary intake and intestinal blood loss. Blood tests to check iron and ferritin levels can be helpful, and ferrous sulphate, given orally, may be recommended to correct any deficit. Some vets routinely supplement CRF patients with a low dose of oral iron although this is usually quite unpalatable so may not be popular with the cat! If gastro-intestinal bleeding occurs, this also requires attention and the use of sucralfate and/or H2-receptor antagonists.
Although anabolic steroids (e.g. nandrolone) are used widely in veterinary practice, they are probably not that effective in treating anaemia caused by CRF.
The value of rHuEPO has been established in several studies, and it has the capacity to dramatically reverse the anaemia and, therefore, have a significant impact on the cat's wellbeing. However, possible benefits of treatment have to be weighed against risk of adverse side-effects and cost of the drug. Complications of rHuEPO therapy include poor response due to iron deficiency (routine iron supplementation may be prudent during therapy), hypertension, polycythaemia (an increase in the numbers of red blood cells in the blood). There is also a risk that the cat will produce anti-rHuEPO antibodies. This latter side-effect is potentially the most important, and is thought to occur in approximately 30% of treated cats, necessitating the withdrawal of treatment. Because of the relatively high prevalence of this complication, rHuEPO therapy is usually reserved for cats with moderate to severe anaemia.
Vitamin D Therapy
Calcitriol (vitamin D therapy) is still a somewhat controversial treatment, although advocated by some veterinarians.
The rationale for its use is that it is an effective treatment for renal secondary hyperparathyroidism (over-production of parathyroid hormone caused by kidney failure), which may play an important role in the removal of waste products from the body, and possibly the progression of renal failure.
Controlled studies to substantiate a beneficial role for this therapy are lacking and further studies are necessary before it can receive strong recommendation.
Other treatments
It is important that the treatment of chronic kidney failure is tailored to the specific needs of each individual cat.
Whilst we have tried to cover the main treatments that are used today, a variety of others may be recommended by your veterinary surgeon, say if your cat suffers from one of the rarer complications associated with kidney failure.
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Feline Kidney Disease
by Dr. Derek Duval, VMD
I received a number of letters requesting information about kidney disease in cats and how diet may be important in its cause and treatment. Many cats will develop renal (kidney) insufficiency as they age. With age the kidneys will loose nephrons (the functional unit of the kidney) and renal failure will result. The kidney (like the liver) has a large built in reserve capacity. By the time we see signs are renal insufficiency 60-75% of the renal mass is lost. The first signs are usually loss of the ability to concentrate the urine which results in increased drinking and urinating. With more damage the toxins that are normally filtered by the kidney begin to build up and can cause depression, decreased appetite, a foul odor to the breath, oral ulceration, and vomiting. In the end stage of renal failure, a low body temperature, seizures, and severe depression and coma can result.
Diagnosis: The most common clinical signs are vomiting, increased urination and increased thirst. If you see these signs have your veterinarian evaluate your cat. (Other disease share these same signs; such as diabetes, hyperthyrioidism ...) The veterinarian should do blood and urine tests. Blood tests that are important are the BUN, Creatinine and phosphorous. BUN or blood urea nitrogen is a chemical that the liver makes from ammonia. Ammonia is absorbed in the gut from the breakdown of dietary protein. After production in the liver, BUN is excreted by the kidneys. BUN increases in other disease states as well including dehydration and urethral obstruction. The creatinine is a breakdown product of muscle and is excreted by the kidney at a constant rate. Although we do not believe it causes problems when it is high, the creatinine serves as an important marker for kidney function. It is also effected less by dehydration and may help us determine if an elevated BUN is due to renal causes or not. In renal failure the phosphorous may increase and lead to mineralization of various sites in the body.
In the urine we look for signs of infection, ability to concentrate, and loss of protein. When cats with healthy kidneys become dehydrated the urine will become concentrated. Cats with renal insufficiency cannot concentrate their urine despite being dehydrated. Therefore, a urine sample is very important to the evaluation of renal disease.
The normal blood and urine values vary from lab to lab, but BUN <30 mg/dl, Crea <2.2 mg/dl, Phos <5 mEq/l, Urine specific gravity >1.018 are relatively normal. Obviously the interpretation of blood and urine values can be quite complicated (that's probably why then send us to school for so long) so seek veterinary advice.
Other modes of evaluating the kidneys include radiography (x-rays), ultrasound examination, and palpation. The kidneys in cats with chronic renal insufficiency are often shrunken and irregular.
Treatment: Treatment of renal failure has three main goals. The first is to keep the BUN and other "uremic" toxins low. Uremic toxins are chemicals and waste products normally excreted by the kidneys. BUN is one of these but it is important to realize it is not the only one. Uremic toxins are responsible for many of the signs of kidney disease. These are kept low with fluid therapy and dietary modification. When cats are ill, intravenous fluids are often required. For long term therapy, fluids can be given under the skin. I've had many owner give their cats fluids under the skin (Sub-Q) and help them manage their renal failure for years. The frequency and amount of fluids that a cat needs depends on the degree of damage to the kidneys. Some cats cannot be managed on sub-q fluids and cannot be managed off of intravenous fluids. I will discuss dietary manipulation separately in a moment. The second goal of renal failure treatment is to limit the phosphorous. Since these chemical can lead to mineralization and a worsening of renal failure it needs to be kept low. If the phosphorous is elevated I generally use drugs that bind the phosphorous in the intestine and do not allow it to be absorbed. Alternagel or other antacid products that bind phosphate are what I recommend. The third goal of therapy is to help prevent stomach ulcers that may occur secondary to the uremic toxins. Drugs that are useful include Tagamet (cimetadine), Zantac (ranitadine), carafate (sucralfate), and cytotec.
Diet is frequently discussed as a possible treatment and as a possible causes in renal failure in dogs and cats. It is true that protein in the diet is converted to BUN by the liver. In that sense minimizing protein may minimize BUN. Unfortunately the degree to which this is effective is probably nonsignificant. In normal dogs restricted protein does decrease the BUN from normal to low normal. In renal failure the BUN may decrease from 100 to 80, but it is still too high. In my opinion, if the BUN is high enough to require therapy, it needs more than dietary modification.
Do high protein diets causes renal failure? No. In dogs they have removed 7/8 of the renal mass and then placed them on diets of various protein level and quality. Dietary protein had no effect on the development of renal failure. In cats similar studies suggest that dietary protein level is not associated with renal failure.
Cats are not small dogs (despite what some of you may think) and have very different medical and physiological parameters. For instance, cats require a higher portion of calories to come from dietary protein. In dogs on low protein diets, they can use other sources (such as fat and carbohydrates) for energy, but because of the peculiarities of cats, cats cannot do this. So not only is protein restriction likely to be nonprotective, but will likely do more harm than good.
What can I do about the diet? Well, diets that are low in potassium can cause renal failure. There have been commercial diets in the past that had been poorly formulated and may have led to the development of renal failure. These diets have been removed from the market and/or reformulated to eliminate this problem. During developing renal insufficiency the phosphate content of the diet may be important. High phosphate levels may lead to worsening renal failure. Many diets today are acidified to help reduce the risk of FUS (or FLUTD as it is now known) this may cause increased loss of potassium in the urine and promote potassium depletion. Currently these problems (high phosphate and acidification) are being investigated in cats to see how important they are to the development of renal failure.
At this point I would not recommend any dietary modification prior to a diagnosis of renal failure or insufficiency. Dietary modification with a relatively low protein diet (20-25%) may help reduce clinical signs of uremic toxins at that point.
Another consequence of chronic renal failure is anemia. The kidneys are responsible for the production of the hormone erythropoetin. This hormone causes the bone marrow to produce new red blood cells. In cats with chronic renal failure this hormone may be deficient. The bone marrow production of red blood cells slows or stops. Since red blood cells are dying every day (normally to be replaced by new ones) an anemia results. The anemia is classified as nonregenerative, meaning that the body is not compensating by creating new cells. The anemia is slow to develop, and cats generally acclimate to the decrease. When the anemia is severe enough however, cats become clinical. Signs of anemia are pale gums, lethargy, depression, and decreased activity. Panting and increased heart rate may result as well. Fortunately, erythropoetin has been recently synthesized recombinately and it is available for use in cats. This medication called Epogen is given by injection multiple times a week and results in good regenerative responses in cats. Unfortunately, about 40% of cats given Epogen will eventually form antibodies against it and then fail to respond. Because of this possibility it is recommended that Epogen therapy be started only after the anemia is in a more severe stage.
The prognosis for cats with renal insufficiency depends on the degree of damage the kidneys have or more importantly, the degree of function they still have left. Fluid therapy and drug therapy can allow cats to leave relatively happy lives for months to a couple of years. Cats that can not be stabilized for home management carry a worse prognosis and euthanasia should be considered. Unfortunately, if a cat lives long enough it will likely have some degree of renal insufficiency. Regular veterinary exams and blood work in older cats may allow us to detect these patients early and keep them happy and comfortable for longer. Other disease that may make renal failure worse are hyperthyroidism, and hypertension.
Derek Duval, VMD Philadelphia, PA
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