Kidney Failure in Cats

Understanding the condition

Kidney failure is a common and important condition, particularly in older cats.  The cat has two kidneys which act as filters to remove waste products from the bloodstream, which are then excreted in the urine.  They also aid in the maintenance of hydration and fluid balance within the body, and regulate the production of certain hormones required for red blood cell formation and vitamin D absorption.

Unlike the liver, which has massive powers of regeneration, if the kidneys are damaged they cannot repair themselves, and ongoing damage or disease results in a deterioration in function.  Kidney failure can be either an acute or chronic process - acute kidney failure can occur after sudden damage such as an infectious disease, physical injury or poisoning; whereas chronic kidney failure is seen as a progressive deterioration of kidney function over a relatively long period of time (typically months to years).  A cat may lose up to 75% of kidney function before symptoms become noticable, at which point the cat may appear to become suddenly ill.

Diagnosis

The kidneys usually act to concentrate the urine according to the cat's hydration status, and the normal feline kidney has very good powers of concentration.  This is performed by the kidney tubules, and once these begin to lose function the cat becomes unable to concentrate its urine so efficiently.  This leads to an increase in urination, and consequently an increase in thirst to maintain the body's hydration status.  This increase in thirst is often the first sign noticed by owners, but it can occur very gradually or be missed in multi-cat households.

When the kidneys are no longer able to filter waste products from the bloodstream efficiently, these waste products build up within the body leading to toxic effects.  These effects may be seen as a loss of appetite or pickiness with food, weight loss, vomiting, smelly breath, poor coat condition and a general lethargy or weakness.  Many of these changes can be put down to 'old age' but may actually be a sign of underlying kidney problems.

Any of these symptoms may prompt you to bring your cat to the vet initially, or they may be noted by the vet during a health check and alert them to the possibilty of underlying disease. In order to diagnose the disease your vet will usually need to perform: 

1. Blood sample - the kidneys usually act to filter the waste products urea and creatinine from the bloodstream. These products are produced when protein is broken down for use within the body. When the kidneys are not working efficiently, the waste products build up in the bloodstream, and can accumulate to toxic levels. The degree of elevation of these products within the bloodstream can give an indication of the severity of disease. In addition, your vet will be able to assess your cat's hydration status, electrolyte levels and phosphate levels from a blood sample. These factors are all important as they can be involved in progression of the disease process.
2. Urine sample - this enables your vet to determine how well your cat is able to concentrate its urine, and whether it is losing protein through its kidneys. In addition cats which are unable to produce concentrated urine are more prone to bacterial infections of the bladder (cystitis), and evidence of this may be seen on a urine sample in the form of blood or inflammatory cells. 

In young cats, or where the condition has appeared very suddenly (ie. acute renal failure), your vet may want to perform further tests to try and establish a cause of the renal failure, in case it can be directly treated.  In older cats or those which have been exhibiting symptoms for some time, it is usually assumed that the condition is chronic and further tests will depend on the suspicion of concurrent disease or associated complications.  Secondary changes which can occur as a result of failure of the kidney's other regulatory functions include anaemia, high phosphate levels, bone demineralisation, high blood pressure and blindness.  These conditions may or may not be identified on presentation or by testing, and require regular monitoring.

Treatment

In some cases a specific cause for the renal failure may be identified, in which case a specific treatment may be implemented (eg. antibiotic treatment for bacterial infection of the kidneys).

However, chronic kidney failure is not a condition which can be cured, but it can be kept under control very well with a few simple measures.  The degree of control which can be established, and hence the prognosis, often depends on how early the disease is diagnosed. Some cats may require initial hospitalisation and fluid therapy to correct dehydration and reduce the waste products in the bloodstream by promoting urination.  Once the cat is stable, home therapy may involve a number of treatment options depending on the severity of your cat's condition and any concurrent disease processes which may lead to ongoing kidney damage:

• Diet - Dietary management is vital to the treatment of all cats with kidney failure. 'Renal' diets aim to provide a small amount of high quality protein, therefore minimising the amount of waste products which need to be excreted through the kidneys. They also restrict phosphate content as cats with kidney failure often develop high phosphate levels in the bloodstream due to a breakdown in the normal hormonal regulation of these levels. In addition, sodium is restricted to control the hypertension (high blood pressure) which often occurs in kidney failure.
• Water intake - cats with kidney failure will often become dehydrated, as the kidneys are no longer able to concentrate the urine (and hence conserve water). Maintaining water intake is therefore very important and free access to water should always be available, in addition it is often wise to feed wet food as cats generally gain much of their water from food.
• 'ACE inhibitors' - these drugs act to dilate blood vessels within the body, including the kidneys, therefore improving blood flow and hence excretion of waste products from the bloodstream. They also help to reduce the loss of protein through the kidneys, and can help if proteinuria is detected in a urine sample.
• Phosphate binders - If phosphate levels remain high despite dietary restriction then binding agents can be added to the food as an additional control. These are available as palatable liquids which can be pumped onto the food.
• Blood pressure tablets - where hypertension is diagnosed in a cat with renal failure it can lead to complications such as bleeding into the eyes or brain, or blindness, in addition to the worsening effect on the kidney function. In these cases tablets may be prescribed to help control the blood pressure.
• Potassium supplementation - cats may develop low potassium levels with renal failure, and where this is identified potassium supplementation can be added to the diet.

Early diagnosis is key to the success of controlling this condition, and when brought under control at an early stage cats may live for many years after diagnosis. It involves a lifelong commitment to treatment and monitoring, but with more advances in research occurring all the time, the outlook for cats with this disease is getting better by the day.

(BL)