Chronic renal (kidney) failure (CRF)

Chronic renal (kidney) failure (CRF) is a common problem in all cat breeds. The digestion of food produces waste products, which are carried by blood to the kidneys to be filtered and excreted in the form of urine. When the kidneys fail, they are no longer able to remove these waste products, and toxins build up in the blood producing clinical signs of kidney disease.

The normal kidney is responsible for filtering the blood and removing metabolic toxins which are excreted in the urine. It plays a crucial part in maintaining water and electrolyte balance in the body. Major roles of the kidney include:

Excretion of waste products
Water balance
Electrolyte balance
Erythropoietin production (hormone causes bone marrow to produce red cells)
Rennin production (hormone helps control blood pressure)
Activation of vitamin D.

The failing kidney is unable to filter the toxins in the blood causing their levels to rise (azotaemia). When this rise in toxins causes clinical signs in the animal it is termed uraemia. The inability to control water balance results in very dilute urine and signs of dehydration.

Reduced erythropoietin secretions can lead to reduced production of red blood cells and subsequent anaemia.

Signs of Chronic Renal Failure in Cats

Polyuria (increased urination)
Polydipsia (increased thirst)
Anorexia
Lethargy
Vomiting
Weight loss
Acute blindness
Dehydration
Oral ulceration
Halitosis

The clinical signs are related to the severity of the renal failure and the presence of complications such as hypertension (high blood pressure). Cats with mild chronic renal failure may not show any signs as long as they are coping with the changes in the kidney (compensating). Occasionally something triggers these cats to become de-compensated and signs of uraemia become apparent. This is termed a uraemic crisis.

Polyuria and polydipsia may only present in up to 40% of cats. The acute blindness is often secondary to hypertension whereby high blood pressure causes damage to the delicate blood vessels in the eye. Halitosis is due to the build up of toxins. Uraemic breath is a term often used to describe the smell associated with these cats. Dental disease can also cause halitosis in cats and this is also commonly seen in older cats so the two must not be confused.

What causes Chronic Renal Failure in Cats?

Most cases of chronic renal failure have a non specific, non identifiable cause. They present as a degenerative disease. Known causes are less common and include congenital renal disease, toxins, pyelonephritis (kidney infection), PKD (polycystic kidney disease), toxic drugs, lymphoma, FIP (feline infectious peritonitis)

Renal failure is usually diagnosed through blood tests. Azotaemia is identified by elevations of two substances, urea and creatinine. These substances are usually excreted into the urine by the kidney and so kidney dysfunction causes a rise in their blood concentration. Other causes of azotaemia must be differentiated from renal failure, these include dehydration and urethral blockage. These other causes are termed pre-renal azotaemia (before the kidney) i.e. dehydration, or post-renal azotaemina (after the kidney) i.e. urethral blockage (blocked bladder)
The blood tests may also show anaemia (reduced red blood cells).

Analysis of urine can support the blood results. A measurement called Urine specific gravity helps establish the concentrating ability of the urine. A failing kidney is unable to concentrate urine and so the Urine specific gravity is low indicating very dilute urine. Urine tests may also reveal protein, another finding in some cases of chronic renal failure.

The kidneys in chronic renal failure are usually smaller than normal apart from polycystic kidney disease and certain cancers where they are larger. Ultrasound examination may reveal changes in the tissues of the kidney which indicates compromised renal tissue.

What is the treatment of Chronic Renal Failure?

The treatment depends on whether the animal is compensating or not. De-compensated cats in uraemic crisis need intravenous fluids to correct fluid and electrolyte imbalances. They will often have to be hospitalised for a number of days. Medications to prevent nausea and vomiting may also be necessary.

Long term management of compensating cats includes:

Increasing water intake
Dietary management
Appetite stimulation
Control of hypertension

Some owners use water drinking fountains to increase water intake or leave a tap dripping in the house since some cats prefer to drink from running water. Feeding wet canned food instead of dry can also increase daily water intake.

Special renal diets are proven to increase life expectancy of cats in chronic renal failure. The main features of a renal diet are reduced protein, sodium and phosphorus. This slows the degenerative change in the kidneys and controls hypertension.

Where there is hypertension, medications to manage blood pressure can be advantageous. Your veterinary surgeon will be able to advise you on this.

Getting your cat to eat is a very important part of managing renal failure. Introducing new diets to a sick cat is not advisable. Gradual introduction when your cat is stabilised is preferred. These diets are often fed for the lifetime of the cat.

Monitoring of Chronic Renal Failure

It is important for you to monitor your cats weight, appetite and water intake as part of long term observations. In addition to this your veterinary surgeon may want to periodically take blood and urine samples to attain kidney function. Blood pressure measurements may also help to obtain an overall clinical picture.

Disclaimer

This pet health article is for reference only.

If your pet is showing any symptoms or distress, and you suspect your pet is ill CONTACT YOUR VET IMMEDIATELY.