Chronic renal failure (CRF) is a common cause of illness in older cats. Unlike some other organs such as the liver, damage to the kidneys cannot be repaired. Signs of renal disease are usually seen once at least 70-75% of the renal tissue has been irreversibly damaged and, once established, CRF is generally a naturally progressive condition. The rate of progression of disease can vary hugely from cat to cat. There is no cure for CRF and in people with this condition, dialysis treatment followed by renal transplantation are the main options. Neither of these treatments are currently available in the UK, although it is possible to improve the quality of life of affected cats by employing a variety of medical treatments tailored according to the individual's needs. In recent years many treatment advances have been made and there are now more options available to owners wishing to care for their cats with CRF. Before discussing these treatments in detail, it is important to consider what normal kidney function is and therefore the range of problems that cats with CRF may have.
In normal cats, the kidneys play many vital roles which include:
Elimination of waste products, drugs and toxins from the body via the urine
Regulation of the body's acidity, electrolyte levels (calcium, phosphate, potassium, sodium and chloride) and water balance
Production of hormones such as erythropoeitin (required to stimulate production of red blood cells by the bone marrow) and renin (important in controlling water and salt balance)
Activation of vitamin D (important in control of blood calcium and phosphate levels)
Regulation of blood pressure
Signs of CRF develop when two thirds to three quarters of renal function has been lost. Cats with CRF are vulnerable to problems including:
Accumulation of protein breakdown products (including urea and creatinine which can be measured in blood samples) which is associated with clinical signs of illness (e.g. nausea, vomiting, loss of appetite)
Acidosis (increased blood acidity)
Anaemia (partly due to lack of production of erythropoeitin)
High blood pressure (systemic hypertension)
CRF cats often show non-specific signs of ill health such as a variable or poor appetite, weight loss, depression and sickness. An increased thirst is seen in about one third of cats with CRF although this clinical sign can also be seen with various other conditions common in middle aged and elderly cats such as hyperthyroidism and diabetes mellitus ('sugar diabetes'). Diagnosis of CRF therefore requires collection of blood and urine samples for analysis. Most commonly a diagnosis is made following identification of azotaemia (accumulation of the protein breakdown products creatinine and urea in the blood) and loss of urine concentrating ability (i.e. the urine is more dilute than it should be). Further tests may be required in some cats to identify the cause of the renal disease. For example ultrasound examination of the kidneys is usually a straightforward technique for identification of polycystic kidney disease (PKD).
Management of cats with CRF involves a range of treatments tailored according to the individual's needs.
What is the ideal diet for cats with kidney problems?
It is common to prescribe specific dietary therapy since this has been shown to improve the quality of life and survival of cats with CRF and may reduce the rate of progression of disease. Renal diets typically have restricted levels of high quality protein which limits the amount of protein breakdown waste products for the ailing kidneys to excrete. Levels of phosphate are also restricted since cats with CRF have a tendency to retain excess amounts of this in the body which can contribute to their feeling unwell. Renal diets have increased amounts of potassium and B vitamins which CRF cats are vulnerable to losing in their urine and increased numbers of calories which helps CRF cats with a poor appetite to maintain a normal body weight. Renal diets usually have lower levels of sodium in them which may help to reduce the risk of high blood pressure developing.
It is possible to prepare home cooked diets for cats with CRF and veterinary recipes are available for this purpose. Most owners do not elect for home cooking protocols as this is very time consuming and therefore not a practical option in most cases.
Cats with CRF often have a poor appetite and this can be exacerbated by offering special kidney diets which may not appeal to the cat. In some cases, the use of appetite stimulants such as the anti-histamine cyproheptidine (trade name Periactin) or anabolic steroids can be helpful in stimulating an adequate appetite. More recently some vets have been treating cats with persistently poor appetites by placing a feeding tube into the stomach. Feeding tubes can be placed into the stomach using endoscopy and are referred to as PEG tubes when this is done (percutaneous endoscopically placed gastrostomy tube). Although an anaesthetic and short period of post-operative hospitalisation is required to place the tube, once in place these can be used for prolonged periods to administer food, liquids and medicines to the cat.
How can dehydration be treated and prevented?
Cats with CRF are vulnerable to becoming dehydrated since they are unable to produce concentrated urine. Encouraging cats to drink and maintain normal hydration is helpful, if possible, and moist diets are probably preferable. Offering flavoured water may encourage cats to drink more (e.g. fish broth) although it is important to not offer salty liquids as these can increase the risk of high blood pressure and other problems developing. Many cats with CRF do however prefer the dry kidney diets and it can be difficult to encourage drinking. In recent years, one treatment that has received a lot of attention is administration of fluids under the skin by the cat's owner (subcutaneous fluid therapy).
This is not currently a common recommendation in the UK although many USA owners of CRF cats are finding it a simple and valuable technique for helping their cat. In severe cases, dehydration may require treatment with intravenous fluid therapy (i.e. cat admitted to a veterinary surgery and placed on a drip). Giving additional fluids at home can therefore be helpful in preventing this. In addition, extra treatments such as potassium can be added to the fluids. Subcutaneous fluid therapy usually involves giving around 150 ml of fluid under the skin twice a week. The technique is well tolerated by most cats and owners include one report of a 19 year old cat with CRF that has been managed for 6 years using subcutaneous fluid therapy as part of the management protocol. If necessary, the regime can be changed to more frequent fluid administration. The owner will be trained in how to perform this technique by a veterinary surgeon or nurse - it is important that the fluid is given correctly in a sterile manner so that infections do not occur at the site of injection. Some cats do not tolerate this procedure and so it may not be suitable for all cats with CRF.
How can electrolyte problems be treated and prevented?
Electrolytes are salts present in the body which are required for normal cellular functions. The most common electrolyte imbalances in CRF cats involve potassium and phosphate. CRF cats are vulnerable to losing potassium in their urine which can cause a reduction in the blood potassium levels (hypokalaemia). Hypokalaemic cats can become very weak and lose their appetite. Although renal diets contain increased amounts of potassium in them, some cats with CRF can still develop low blood potassium levels. Additional potassium can be supplied to these cats as a powder, tablet or liquid.
CRF cats are vulnerable to accumulating phosphate which can make them hyperphosphataemic (have high blood phosphate levels). Oral phosphate binders are drugs which bind to phosphate present in the diet and limit what is absorbed by the cat's bowel. These drugs may be needed in CRF cats whose blood phosphate levels stay high in spite of dietary therapy or in those cats that will not eat a prescription diet.
How can systemic hypertension be treated and prevented?
High blood pressure (hypertension) occurs in 20 - 30% of cats with CRF and can have serious consequences such as blindness. Monitoring of blood pressure is therefore important so that high blood pressure can be identified and treated rapidly where it occurs. Most practices now have facilities to measure blood pressure in cats and this is a technique which is simple, pain free and only takes a few minutes to perform. In those cats requiring treatment, anti-hypertensive drugs (such as oral amlodipine or benazepril) can be prescribed. Most cats need once daily therapy to maintain normal blood pressure.
What other treatments may be needed?
Additional treatments which may be prescribed according to the needs of the cat include:
Erythropoietin: Anaemia is common in cats with CRF and one reason for this is the decreased amounts of erythropoietin produced by the kidneys. Erythropoietin is a hormone that triggers red blood cell production by the bone marrow and treatment of anaemic CRF cats with human erythropoeitin can be helpful in reversing the anaemia. Unfortunately, this treatment can be expensive and may not always have a lasting effect as the human hormone is recognised as a foreign substance by the cat's body which eventually produces antibodies to the drug preventing it from having a useful effect. Another possible side effect of this treatment is development or exacerbation of high blood pressure so cats receiving this treatment need to be carefully monitored. There is research underway in two US universities to develop a feline erythropoietin which would be much more helpful and should not result in antibody production by the cat.
Iron supplementation: Some anaemic CRF cats are iron deficient so measuring iron status and considering iron supplementation may be useful. Iron is required in production of haemoglobin, the oxygen carrying molecule in red blood cells.
Anti-sickness pills for vomiting: cats with CRF may suffer from what is known as uraemic gastritis (inflammation of the stomach due to retention of waste products and hormones which the kidneys normally excrete). Anti-sickness treatments including antacids and anti-vomiting drugs can be very helpful at treating this problem which may help the cat to feel much better.
Prevention and treatment of acidosis: Cats with CRF are vulnerable to becoming acidotic (ie their blood is more acid than it should be). This has many consequences all of which make the cat feel more unwell. Where at all possible, cats with CRF should not be fed acidifying diets (these diets are often prescribed for cats with lower urinary tract problems such as cystitis and bladder stones) as this increases the likelihood of acidosis. Treatment for acidosis involves use of drugs like sodium bicarbonate.
Calcitriol (vitamin D therapy). Although still somewhat controversial, many clinicians have used this treatment in certain selected CRF patients and found it beneficial at maintaining normal blood levels of calcium and phosphate.
ACE (angiotensin converting enzyme) inhibitors such as benazepril (Fortekor®, Novartis): This treatment has recently been advocated based on research in people with CRF in which ACE inhibitors were found to increase the survival times. Data from a recent clinical trial in cats with CRF suggested that cats receiving this therapy had a better quality of life (as assessed by their owners), a reduction in the amount of protein they were losing in their urine and slightly increased survival times. Fortekor did not reduce the parameters used to assess renal function (e.g. blood urea and creatinine levels). In the same clinical trial, a specific sub-set of cats with CRF which were losing large amounts of protein in their urine showed an excellent response to Fortekor® treatment (dramatically improved survival, appetite and weight gain). Unfortunately this manifestation of CRF accounts for only a small proportion of all cats with CRF.
ACE inhibitors also lower the blood pressure and so may be prescribed as anti-hypertensive therapy.
Antibiotics: recent studies showed that up to 30% of cats with CRF suffer from a bacterial cystitis at some point in the course of their disease. In some cats this infection may spread to the kidneys further compromising the renal function. In other cats, the bacterial cystitis is a consequence of bacterial infection of the kidneys (pyelonephritis). Cats with CRF may be more vulnerable to the development of bacterial urinary tract infections since the urine they are producing is so dilute. Unfortunately, in many cases the bacterial infection does not cause signs of cystitis (such as urinating more frequently, straining to urinate and passing bloody urine) which makes diagnosis of this complication difficult. Diagnosis requires collection of a urine sample which is assessed for microscopic evidence of bacteria and inoculated onto bacterial culture media for growth in a laboratory. A course of antibiotics, in some cases for weeks or months, may be needed to successfully eliminate bacterial urinary tract infections.
Other medications not discussed may be required in some cats with CRF and it is important to modify the treatment according to the specific requirements of each individual cat. The FAB website (http://www.fabcats.org/) contains useful information on renal disease as does the following web site which was designed by an owner of a cat with CRF http://www.felinecrf.com/