Kidneys have many functions, they principally act to remove waste products from the blood stream, maintain essential nutrients e.g. potassium at the correct level, maintain hydration and produce urine.
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 clinical signs are seen. In many cases this means that the damage to the kidneys has been occurring over a number of months or years (chronic) before failure is evident. As chronic renal failure (CRF) is most commonly seen in old cats (though 10% of cases occur in cats under 3 years old), early signs of disease such as weight loss and poor coat quality are often put down to normal ageing changes. 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), at some point this is no longer possible resulting in a relatively rapid rise in waste products in the bloodstream and an apparent sudden onset of severe disease.
A large number of different processes can eventually lead to CRF including:
CRF is therefore the end stage of a number of different disease processes rather than a specific condition it its own right.
Renal failure is usually diagnosed by looking 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. It is also diagnosed by measuring the ‘specific gravity’ of the urine (the concentration) and if the cat has chronic renal failure it is normally less than 1.030.
Unfortunately this is very difficult as neither clinical signs of renal failure nor rises in BUN and creatinine are evident until significant loss of kidney function has occurred. In the earlier stages of disease there are no clinical signs to indicate that sophisticated renal function tests, which can pick up early renal damage, are required.
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. Cats are often seen to drink and urinate more and some will have vomiting and diarrhoea. Rarely renal failure is seen as sudden onset blindness.
Depending on the results of blood tests your veterinary surgeon may be faced with several problems which require different treatments. Don’t worry if the list below seems so long that you 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.
Increasing water intake is very important. Cats should be encouraged to drink as much as possible using different bowls, pet ‘fountains’ etc.
I/V fluids: often used initially to rehydrate and lower the level of waste products in the bloodstream while medical management is started/instigated.
Owners can also be shown how to give fluids to their cat under the skin.
Lowering the level of waste products in the bloodstream can be achieved by low protein and low phosphorus diets. These are available ready prepared from your veterinary practice. 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.
Phosphate binders: despite low phosphate in the diet, blood phosphorus levels 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.
Antibiotics: many cats seem to respond to antibiotics though the reason for this is not always clear.
Potassium supplementation: cats in renal failure tend to loose too much potassium in the urine this leads to muscle weakness, stiffness and poor hair quality. Low potassium may also contribute to the worsening of kidney failure.
Vitamins B and C: these vitamins are wasted by the kidney and may need daily supplementation.
Anti-emetics: for those cats that are being sick, use of anti-emetics reduces the feeling of nausea thereby improving appetite.
Hypotensive drugs: significant numbers of cats have high blood pressure because of their renal failure, in some cases lowering their blood pressure may be necessary.
(Treatment of anaemia: the kidneys also have a function to initiate the production of red blood cell in the bone marrow. Many cats with CRF are anaemic due to a lack of stimulation of marrow. Stimulation of the marrow can be achieved by the use of some anabolic steroids in high dosages.)
IT IS IMPORTANT THAT FRESH WATER IS AVAILABLE AT ALL TIMES AS CATS WITH RENAL FAILURE TEND TO DEHYDRATE RAPIDLY.
Unfortunately, once damaged the kidneys have a very limited ability to recover, but progress of disease may be very slow so, with treatment, your cat may have several years of good quality, active life ahead.
Should you wish to discuss any of these issues in more detail, please consult your veterinary surgeon.