What do my cat’s kidneys do?
Kidneys have many functions. However, their MAIN role is to remove nitrogenous waste products from the blood stream, maintain essential nutrients (e.g. potassium at the correct level), maintain hydration and produce a small amount of very concentrated urine.
What is chronic renal disease?
The kidneys have a large amount of spare capacity to perform their various functions so at least 70% of the kidneys need to be dysfunctional before any clinical signs are seen.
In many cases, when the FIRST signs are seen this means that the damage to the kidneys has been occurring slowly over a number of months or years (chronic) before ‘damage’ is evident.
As chronic renal disease (which eventually leads to renal failure CRF) is most commonly seen in older cats, early signs of disease such as weight loss, increased thirst and poor coat quality are often put down to the normal ageing process.
In the initial stages of disease the kidneys cope with their inability to concentrate waste products by excreting them at a lower concentration over a larger volume (compensated renal failure).
In simple terms, this means drinking more and then urinating larger amounts of ‘weak’ or ‘dilute’ or unconcentrated urine.
At some point this increased drinking and weeing is no longer controls the disease and this results in a relatively rapid rise of waste products in the bloodstream and an apparent sudden onset of severe disease.
i.e. – an apparently healthy cat will suddenly ‘crash’ – much to their human family’s shock and distress.
What are the causes of CRF?
A large number of different disease processes can eventually lead to CRF including:-
1. Congenital malformations of the kidneys – e.g. polycystic kidneys in long haired cats. Many of these cats will develop the disease at a very young age.
2. Bacterial infections (pyelonephritis).
3. Glomerulonephritis – damage to the filtration membrane.
4. Neoplasia – various tumours of the kidney are seen, most commonly lymphosarcoma.
5. Amyloidosis – this is the build-up of an unusual material in the kidney which prevents the kidney from functioning normally.
6. Viral infections e.g. feline immunodeficiency virus or feline infectious peritonitis virus.
7. The highly ‘specialised’ nature of a cat’s kidneys compared to that of a dog or a horse. Cats are originally desert animals and are therefore their kidneys are highly adapted to conserving water. This high degree of specialisation also means that cats’ kidneys can wear out much faster and more easily than those of other species
End-Stage Disease: CRF is therefore usually the end stage of a number of different disease processes rather than a specific condition in its own right.
How is the disease diagnosed?
The first clue that your cat may have renal disease is the clinical signs mentioned earlier; increased thirst and urination, weight loss, stark and dry coat, possible mild constipation and maybe occasional vomiting.
Actual renal disease or possibly renal failure is diagnosed by performing blood and urine tests.
The most common blood tests look at the level of two waste products in the bloodstream, blood urea nitrogen (BUN) and creatinine.
Tests to measure the blood levels of other substances e.g. potassium, phosphorus and calcium as well as the red and white blood cell counts can also be important in order to determine the best course of treatment.
Urine tests are performed to measure the ability of the kidneys to concentrate urine.
As a cat develops renal disease, the ability of the kidneys to concentrate urine decreases slowly and progressively.
These changes occur FAR EARLIER than any changes to blood tests.
Could the renal failure have been diagnosed earlier?
Unfortunately this is very difficult as neither clinical signs of renal disease nor rises in BUN and creatinine are evident until significant loss of kidney function has occurred.
However there are quite a number of very simple test which can be performed regularly on a ‘normal’ cat to identify the very early signs of kidney damage – long before changes to BUN or creatinine.
This then allows early preventative measures to be taken.
As mentioned above – testing the Specific Gravity of the urine (USG) is a VERY sensitive and early indicator of renal disease. This test is also very inexpensive and results are available within 5 minutes.
Then we have a new test called SDMA. It is a blood test and also an early indicator of renal disease. Again this test is very inexpensive. SDMA is commonly run combined with a T4 (thyroid function test – see the article on Hyperthyroidism).
And lastly we can measure your cat’s Blood Pressure. An increase in blood pressure occurs commonly in cats with renal disease. Once again, this change is a great early warning sign and can occur well in advance of increases of BUN or creatinine. This is again a very simple test to perform, results are available immediately and it very inexpensive.
At HIGHlands Veterinary Hospital, we regularly perform these tests on our ‘senior’ cats.
And they are THE core monitoring tests that are used for EVERY cat that is in out Feline Wellness Program.
How does CRF affect my cat?
Because the kidneys perform a variety of different functions, the clinical signs of renal failure can be somewhat variable.
The most common changes seen are weight loss, poor hair quality, halitosis (bad breath), variable appetite which may be associated with mouth ulcers, lethargy and depression.
Most cats will drink and urinate more and some will have vomiting and diarrhoea. Some will have constipation.
Rarely renal failure can cause a sudden onset of blindness.
What treatments are available?
Depending on the results of the blood tests we’ll be faced with one or more of several different problems which require different treatments.
Don’t worry if the list below seems so long that your will never be able to administer all the medication, the majority of cats can be effectively managed with diet change including supplementation and one or two other treatments.
1. Lowering the level of waste products in the bloodstream can be achieved by low protein and low phosphorus diets. These can be prepared at home or are available ready prepared commercial from us. The palatability of reduced protein diets is usually not as high as normal cat food, so you may have to persevere for a while before your cat will eat it.
2. Phosphate binders – despite low phosphate in the diet, blood phosphorus levels may remain above normal in some cats. Reducing blood phosphorus can have a major effect on improving your cat’s well-being and slowing disease progression. Phosphate binders e.g. aluminium hydroxide are given by mouth to further lower the amount of phosphorus absorbed through the gut wall.
3. Antibiotics – many cats seem to respond well to antibiotics though the reason for this is not always clear.
4. Potassium supplementation – cats in renal failure tend to lose too much potassium in their urine this leads to muscle weakness, stiffness and poor hair quality. Low potassium may also contribute to the worsening of the kidney failure.
5. Water soluble vitamins B and C – these vitamins are excreted through, wasted by the kidney and often need daily supplementation.
6. Hypotensive drugs – significant numbers of cats have high blood pressure because of their renal failure. This needs to be checked and if it exists, then lowering their blood pressure may be necessary.
7. Appetite stimulants – advancing renal disease greatly impacts a cat’s willingness to eat, that combined with the new diet creates a big problem with many cats just not wanting to eat. This decreased calorie intake further progresses the renal disease.
Fortunately there are two or three excellent appetite stimulants which in most cases will have these cats eating exceptionally well.
8. Increasing blood flow to the kidneys – ‘Benazepril’—a vasodilator that increases the blood flow to the kidneys and help them function more efficiently is one of the mainstays of treating cats with renal disease.
9. Treatment of anaemia – the kidneys also have a function in initiating the production of red blood cell in the bone marrow. Many cats with CRF are anaemic due to a lack of stimulation of the marrow. Arguably, stimulation of the marrow may be achieved by the use of some anabolic steroids in high dosages – however this treatment is no longer in common use.
More recently, however, the hormone (EPO) that the kidney itself produces to stimulate the bone marrow has become available and generally produces a better and more reliable increase in the red blood cell count although it is very expensive and difficult to obtain in Australia.
Above I’ve listed the treatment options which are available to treat and manage chronic renal disease.
However, in the ACUTE situation, when the cat is not eating or drinking and is collapsed, the cat MUST be hospitalised and treated appropriately. Home treatment in these situations is not appropriate and doomed to failure.
IT IS IMPORTANT THAT FRESH WATER IS AVAILABLE AT ALL TIMES AS CATS WITH RENAL FAILURE TEND TO DEHYDRATE RAPIDLY.
What is the cost of treatment?
Treatment costs will vary considerably with each individual case. In the majority of cases long term management is unlikely to cost more than a few cups of coffee a week. In other words, it is more than affordable by most households.
How long can I expect my cat to live?
Unfortunately, once damaged the kidneys have a very limited ability to recover but with appropriate treatment the progress of disease may be very slow indeed, so with treatment, your cat may have several years of good quality, active life ahead.
As you might expect, the earlier the problem is diagnosed and the earlier treatment starts, the longer you can expect your feline friend to survive.
Are kidney transplants available for cats?
A Queensland practitioner used to have a renal transplant programme for cats. Unfortunately this programme is no longer available in Australia
You now have an excellent insight into this very common disease of the older cat.
My take-home message is this; if your cat is showing ANY of these clinical signs, weight loss in spite of ravenous appetite, excessive thirst and urination, vomiting, diarrhoea, panting, restlessness or hyperactivity, cranky or even nasty behaviour and excessive vocalization at night, then one of the first things to consider is that your cat has an overactive thyroid…
Bring your cat in to see us so that we can run a very simple blood test to rule this disease in or out. And then if s/he has an overactive thyroid, we can discuss which form of treatment will work best for you and you feline companion.
The good news is that very soon you’ll have your ‘old’ friend back!