CHRONIC KIDNEY DISEASE IN CATS (“Chronic Renal Insufficiency”)

 

What do my cat's kidneys do ?

Kidneys have many functions but they basically filter the blood, returning filtered blood to the blood stream and excreting filtered wastes by producing urine. Important in this process are:

  1. removal of nitrogenous waste products (mainly urea and creatinine) from the blood stream
  2. maintenance of essential nutrients e.g. protein and potassium at correct concentrations in the blood stream and body
  3. maintenance of normal hydration by producing appropriately concentrated urine
  4. help in controlling blood pressure, produce vital hormones and enzymes and contribute to the production of red blood cells.

What is chronic kidney disease ? 

Chronic renal insufficiency occurs when the kidneys deteriorate gradually over time, losing their ability to function efficiently. The kidneys have a large amount of spare capacity to perform their various functions so some 70% of the kidneys may 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 symptoms are evident. 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”). Thus we may have a cat that shows no obvious symptoms apart from increased water intake and increased volume of urination. Because protein may be lost in the inefficient filtering process there may be gradual weight loss.

Eventually this type of compensation can no longer cope and accumulation of toxic products in the blood begins to occur resulting in uraemia (or azotaemia) and a more rapid deterioration in the affected patient and finally to renal failure.

What are the symptoms ? 

During the compensated phase there will be increased water intake and increased urine volume but this change may initially be so gradual as to go unnoticed. If protein is being lost there will be gradual weight loss as well. As chronic kidney disease is most commonly seen in older cats, early signs of disease such as weight loss and poor coat quality are often put down to normal ageing. Water intake will usually increase quite markedly as the limits of compensation are reached. As the concentrating ability of the kidneys declines the patient may become clinically dehydrated despite drinking large amounts of water.

Once the threshold is reached where compensation can no longer cope, there will be build up of toxic urea, creatinine and probably phosphorus in the blood stream which will cause poor appetite, rapid weight loss and then vomiting, dehydration and rapid deterioration.

How is a diagnosis made? 

The symptoms of renal failure can be similar to those caused by other conditions such as diabetes, liver disease, hyperthyroidism (overactive thyroid glands) or neoplasia (cancer) so definitive diagnosis needs to be arrived at by laboratory confirmation.

  1. Blood screening – will usually reveal increased urea and creatinine. There may also be increased phosphorus levels and anaemia present. There is now a new blood test "SDMA" (symmetric dimethylarginine) available which can detect the very early stage of decreased kidney function.
  2. Urine testing - specific gravity (urine concentration) can assess kidney concentrating ability and is a very useful diagnostic tool especially in the early (compensated) phase of the disease. Simple in-house tests will also detect increased levels of protein and may also point to other possible causes of urinary tract problems by checking glucose and ketones (for diabetes), blood (for inflammation) and white blood cells (for infection). 

What are the causes of CKD ?

A large number of different disease processes can eventually lead to CKD. Congenital malformations of the kidneys ( e.g. polycystic kidneys in long haired cats), bacterial infections (pyelonephritis), glomerulonephritis (inflammatory damage to the filtration membrane), neoplasia (tumors) and viral infections can all contribute although the cause is not always clear. What we do know is that CKD is much more common in older cats than it is in other species such as dogs.

Could the kidney disease have been diagnosed earlier ?

Before the availability of the SDMA test it was very difficult as neither clinical signs of renal failure nor rises in urea and creatinine are evident until significant loss (60-70%) of kidney function has occurred. SDMA can detect very early loss (from 25%) of kidney function. In earlier stages of disease there are no clinical signs to indicate that renal function tests, which can pick up early renal damage, are required. Hence regular routine blood screening may be beneficial especially in older cats to detect any early loss in kidney function.

How does Chronic Kidney Disease 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 marked increase in water consumption, weight loss, decreased appetite and occasional vomiting. Poor hair quality, halitosis (bad breath),  mouth ulcers, lethargy and depression may also occur. Rarely renal failure is seen as sudden onset blindness triggered by increased blood pressure causing  retinal detachment.

 What treatments are available ?

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.

  1. Dietary modification - probably the mainstay of the conservative medical measure available. Lowering the level of waste products in the bloodstream can be aided by introducing a low protein and low phosphorus diet, and what protein is present should be of high quality. The harmful urea and creatinine that accumulate in the blood are by-products of protein metabolism so the less protein in the diet, the less urea and creatinine are created. These types of specialised diets are available as commercial prescription diets (such as Hills k/d) from veterinary practices. The palatability of reduced protein diets may not be 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 special diets, blood phosphorus levels remain above normal in some cats. Reducing blood phosphorus may assist in improving your cat's well being and slowing disease progression. Phosphate binders (specially formulated for renal failure) are given by mouth (or mixed in the food) to further lower the amount of phosphorus absorbed through the gut wall if dietary management alone is not sufficient.
  3. Hypotensive drugs - significant numbers of cats have high blood pressure because of their renal failure. Drugs from a group known as ACE inhibitors may help to improve life expectancy for these cases. 

IT IS IMPORTANT THAT FRESH WATER IS AVAILABLE AT ALL TIMES AS CATS WITH RENAL 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 progression of disease may be very slow so that with appropriate management your cat may have several years of good quality, active life ahead. More recent studies suggest that the most important factor in extending life expectancy is dietary management.