What Healthy Feline Kidneys Do
Kidney failure is one of the most common health problems suffered by cats, particularly as they grow older.
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 veterinarian. 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.
Blood tests
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.
Other Conditions Related To Kidney Failure In Cats
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.
- Kidney Disease
Kidney failure is one of the most common health problems suffered by cats, particularly as they grow older.
But there have been a number of exciting scientific developments in recent years and there are now ways of slowing the progression of the disease. Perhaps more importantly, new treatments can improve the quality of life for a loved pet suffering from kidney failure.
The purpose of this site is to explain the most common causes of kidney failure in cats, and the latest treatments available today.
The signs of kidney failure may include
- excessive thirst and urination
- loss of appetite
- weight loss
- weakness or lethargy
- nausea and vomiting
- mouth ulcers and halitosis (smelly breath)
- poor coat condition
- signs associated with high blood pressure (visual disturbances, behavioural changes)
If your cat is showing any of these signs please consult your veterinarian immediately!
If your cat has already been diagnosed with kidney failure, we hope that this site will help you gain a better understanding of the condition.
- 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 veterinarian. 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 veterinarian is simple, quick, non-invasive and can be carried out at low cost. What's more, it'll give your veterinarian 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 veterinarian. 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 veterinarian 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, veterinarians can confirm a diagnosis of kidney failure by analysing blood for increased levels of two waste products: urea and creatinine.
Again, it is 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 veterinarian.
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 veterinarian.
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.
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
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 veterinarian. This information is therefore provided only to help you better understand the recommendations made by your veterinarian.
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 veterinarian.
- Kidney Diets Explained
Special 'renal' diets are often prescribed for cats with chronic kidney disease (CKD). There is now plenty of good scientific evidence to show that CKD 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.
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.
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.
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.
Increased potassium and vitamin B
Prescription renal diets are supplemented with potassium and water soluble vitamins (B and C vitamins) which CKD cats are vulnerable to losing in their urine. Potassium deficiency is covered in greater depth in the section: Managing potassium deficiency.
Prescription renal diets are supplemented with potassium and water soluble vitamins (B and C vitamins) which CKD 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.
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 CKD cats with a poor appetite to maintain a normal body weight.
Increased palatability and calorie density helps CKD cats with a poor appetite to maintain a normal body weight.
Acid-base balanceRenal diets are formulated to help prevent acidosis (excess blood acidity - a common consequence of kidney disease) from developing in cats with CKD.
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.
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. ACE inhibitors reduce the pressure within the glomerulus of the kidney (the kidney's filter) which is thought to slow down further damage to the kidney. One ACE inhibitor has now been licensed for use in the management of kidney failure in cats.
Cats with CKD tend to develop proteinuria (the presence of protein in the urine) and it has been found that the higher the level of proteinuria, the shorter the expected survival. ACE inhibitors have been shown to significantly reduce the level of proteinuria in cats, just as they do in humans, and treatment tends to improve survival.
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. In clinical trials owners tended to report better quality of life in cats treated with an ACE inhibitor than those treated with just a kidney diet. Additionally appetite was often improved and, indeed, one ACE inhibitor has been shown to increase appetite, even in normal cats.
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 CKD cats.
ACE inhibitors are used to treat mild hypertension but additional anti-hypertensive drugs may be needed in CKD cats suffering from severe hypertension.
- Introduction
- Anorexia
- Nausea & Vomiting
- Constipation
- Potassium Deficiency
- Phosphorous
- Hypertension
- Antibiotics
- Acidosis
- Anaemia
- Vitamin D
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 above is not exhaustive, and your veterinarian may recommend other therapies.
Special Thanks to Novartis Animal Health Inc.
