What do my cat’s kidneys do?
Kidneys have many functions, they principally act to remove nitrogenous waste products from the blood stream, maintain essential nutrients e.g. potassium at the correct level, maintain hydration and produce urine.
What is chronic kidney disease?
The kidneys have a large reserve capacity to perform their various functions, at least 70% of their functional cells need to be destroyed 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 before failure is evident. As CKD is most commonly seen in old cats, early signs of disease such as weight loss and poor coat quality are often put down to normal ageing. 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 which results in a relatively rapid rise in waste products in the bloodstream and an apparent sudden onset of severe disease.
What are the causes of CKD?
A large number of different disease processes can eventually lead to CKD including:-
- Congenital malformations of the kidneys – e.g. polycystic kidneys in long haired cats
- Bacterial infections (pyelonephritis)
- Glomerulonephritis – damage to the filtration membrane
- Neoplasia – various tumours of the kidney are seen, most commonly lymphosarcoma
- Amyloidosis – this is the build up of an unusual material in the kidney which prevents the kidney from functioning normally.
- Viral infections e.g. feline immunodeficiency virus (FIV) or feline infectious peritonitis virus (FIP)
CKD is therefore the end stage of a number of different disease processes rather than a specific condition in its own right.
How is the disease diagnosed?
Kidney failure is usually diagnosed by looking at the level of two waste products in the bloodstream, blood urea (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.
Could the kidney failure have been diagnosed earlier?
Unfortunately this is very difficult, as clinical signs of kidney failure or rises in BUN and creatinine are not 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.
How does CKD 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 (with or without mouth ulcers), variable appetite, lethargy and depression. Less commonly cats are seen to drink and urinate more and some can have vomiting and diarrhoea. Rarely, renal failure is seen as sudden onset blindness.
What treatments are available?
Depending on the results of blood tests your veterinary surgeon may be faced with several problems which require different treatments. Whilst the following list is long, the majority of cats can be effectively managed with diet change including supplementation and one or two other treatments.
- Lowering the level of waste products in the bloodstream can be achieved by low protein and low phosphorus diets. 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. Ask us for the best, most appropriate food for your cat.
- ACEI’s (e.g. Fortekor) – ACE inhibitors are drugs that form a key part in slowing the progression of kidney disease. Since their introduction a significant improvement in the quality and quantity of renal patients’ lives has come about. ACEIs have multiple including reducing protein loss via the kidneys, regulating the blood pressure in the kidneys, and some regulatory effects of the body’s blood pressure.
- Hypotensive drugs (e.g. Amlodipine) – significant numbers of cats have high blood pressure because of their renal failure, in some cases lowering their blood pressure may be necessary.
- Phosphate binders (e.g. Ipakitine) – 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.
- Potassium supplementation (e.g. Hypokal) – cats in renal failure tend to lose too much potassium in the urine, this leads to muscle weakness, stiffness and poor coat quality. Low potassium may also contribute to worsening of the kidney failure.
- Treatment of anaemia – the kidneys also produce a substance that facilitates the production of red blood cells in the bone marrow. Many cats with CKD are anaemic due to a lack of stimulation of the bone marrow. Stimulation of the bone marrow can be achieved by the use of vitamin B12 injections and recombinant human EPO (erythropoietin).
IT IS IMPORTANT THAT FRESH WATER IS AVAILABLE AT ALL TIMES AS CATS WITH KIDNEY FAILURE TEND TO DEHYDRATE RAPIDLY.
How long can I expect my cat to live?
Unfortunately once damaged, the kidneys have a very limited ability to recover but progress of disease may be very slow. Therefore with treatment, your cat may have several years of good quality, active life ahead.