What do my cat’s kidneys do?

The kidneys have many functions. They principally act to remove waste products from the blood stream, balance essential nutrients such potassium and phosphorus at the correct level, maintain hydration and produce urine.  

What is chronic renal failure?


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 this means that the damage to the kidneys has been occurring over a number of months or years (chronic) before failure is evident. Chronic renal failure (CRF) is most commonly seen in older cats. Only about 10% of the cases occur in cats less than three years old. Early signs of disease such as weight loss and poor coat quality are often dismissed as normal aging changes. In the initial stages of kidney disease, the kidneys lose their ability to save water for the body.  They produce large volumes of dilute urine, and the cat must drink large amounts to stay well hydrated. This is known as compensated renal failure. After approximately 70% of the kidney tissues are destroyed, the kidneys can no longer filter all of the waste products from the blood, and there is a rapid rise in toxic products in the bloodstream and an apparent sudden onset of severe disease.


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 – such as polycystic kidneys in long haired cats
  2. Bacterial kidney infections called pyelonephritis
  3. Glomerulonephritis – damage to the kidney’s filtration membrane
  4. Neoplasia – various tumors of the kidney, most commonly lymphosarcoma
  5. Amyloidosis – this is the build-up of an unusual protein in the kidney that prevents the kidney from functioning normally
  6. Viral infections such as feline leukemia virus (FeLV) or feline infectious peritonitis virus (FIP)
  7. CRF is the end stage of a number of different disease processes rather than a specific condition in its own right.


How is the disease diagnosed?


Renal failure is usually diagnosed by looking at the level of two waste products in the bloodstream, blood urea nitrogen (BUN) and creatinine, in conjunction with the concentration  (specific gravity) of the urine. Tests to measure the blood levels of other substances such as potassium, phosphorus and calcium as well as the red and white blood cell counts are important in order to determine the extent of failure and the best course of treatment.


Could the renal failure have been diagnosed earlier?


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 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. We recommend that all senior pets have at least a urinalysis performed every six to twelve months to diagnose kidney disease at it earliest detectable level. A low urine specific gravity may indicate that at least two-thirds of the kidney tissues are damaged.


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. Less commonly, cats are seen to drink and urinate more and some will have vomiting and diarrhea. Rarely, renal failure is seen as sudden onset blindness due to associated hypertension.


What treatments are available?


Depending on the results of blood tests your veterinarian may be faced with several problems that require different treatments. Don’t worry if the list below seems so long that you will never be able to administer all of the medications. The majority of cats can be effectively managed with diet change including supplementation and one or two other treatments.


*Fluid therapy  Because cats with CRF lose large amounts of water through their urine, they can dehydrate very quickly.  It is essential that fresh water be readily available at all times, and the cat is drinking without vomiting.  Often fluid supplementation in the form of intravenous or subcutaneous fluids is the basis of treatment.


*Renal Diets Lowering the level of waste products in the bloodstream by feeding low protein and low phosphorus diets.  A variety of renal diets are available from the Cat Clinic of Cobb.


*Antacids  The toxins that build up with CRF are acids, and when combined with the normal acids in the stomach they can cause significant nausea and gastric reflux.  Many CRF cats feel better and eat better on antacid therapy.


*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 such as aluminum hydroxide are given by mouth to further lower the amount of phosphorus absorbed through the gut wall.


*Antibiotics  On the possibility that an infection in the kidneys may have pushed a cat with compromised renal function out of control,  antibiotics are often used in the treatment of CRF.


*Potassium supplementation  Cats in renal failure tend to lose too much potassium in the urine. This leads to muscle weakness, stiffness and poor hair quality. Low potassium levels may also contribute to the worsening of the kidney failure.


*Anti-emetics  For those cats that are experiencing vomiting, the use of anti-emetics reduces nausea, thereby improving appetite.


*Blood-pressure lowering drugs  Significant numbers of cats with kidney failure have high blood pressure. In some cases lowering their blood pressure may be necessary.


*Treatment of anemia  The kidneys also initiate the production of red blood cells in the bone marrow. Many cats with CRF are anemic due to a lack of stimulation of the bone marrow.  Drugs are available to help stimulate the bone marrow to release more red blood cells into the circulation.


*Cardiac drugs  In some cases cardiac medications are used to improve blood flow to the kidneys and therefore improve kidney function.


What is the cost of treatment?


Treatment costs will vary with each individual case. In the majority of cases, long term management at home is generally inexpensive.


How long can I expect my cat to live?

Unfortunately, once the kidneys are damaged, they have very limited ability to recover. Most CRF cases progress very slowly. With treatment, your cat may have several years of good quality, active life ahead.