CHRONIC KIDNEY DISEASE IN CATS
Chronic kidney (or renal) disease (CKD) is one of the most common conditions affecting older cats. It usually get worse with time, although the rate varies between individuals. Appropriate treatment and support can slow disease progression and increase quality of life.
WHAT DO THE KIDNEYS DO?
They perform a wide variety of roles, including removing toxins from the blood, maintaining salt and water balance, controlling blood pressure, regulating blood acidity and stimulating red blood cell production. Fortunately the kidneys have considerable reserve capacity, so signs of renal failure do not develop until approximately two thirds to three quarters of the total functioning kidney tissue is lost.
WHAT IS CHRONIC KIDNEY DISEASE?
CKD occurs when there is long-standing, irreversible damage to the kidneys. Typically fibrous tissue gradually replaces the normal kidney tissue, and this impairs their ability to filter and remove waste products from the blood.
In most cases the exact cause is unknown, and most cats present in a late stage of the disease, so treatment is aimed at management rather than cure. Where an underlying cause can be identified, and if this is treatable, there is occasionally potential to halt disease progression. There are some well-recognised causes of CKD which include:
- Polycystic kidney disease - an inherited condition seen mainly in Persian and Exotic cats where normal kidney tissue is gradually replaced by multiple fluid-filled cysts.
- Kidney tumours e.g. lymphoma (a solid tumour of white blood cells)
- Infections - bacterial infections of the kidneys (pyelonephritis) may occur as an extension of bladder infections and can lead to sufficient damage to the kidneys to cause failure.
- Other causes - damage by toxins (e.g. antifreeze, lillies), defects in the development of the kidneys at birth, persistent inflammation.
WHAT ARE THE CLINICAL SIGNS?
In most cases, disease onset is gradual, although occasionally the signs may appear to develop quite suddenly. Many of the clinical signs are quite vague and non-specific, the most common ones are:
- Increased thirst and urination (due to an inability to concentrate the urine)
- Poor appetite and weight loss
- Dehydration, lethargy, depression, weakness
- Vomiting, foul smelling breath, mouth ulceration
- Poor coat
Given the diverse functions of the kidneys, a wide variety of complications can arise:
- Electrolyte abnormalities (e.g. low potassium, high phosphate)
- Retention of too much acid (acidosis)
- High blood pressure (hypertension)
- Anaemia (low red blood cell count)
HOW IS CHRONIC KIDNEY DISEASE DIAGNOSED?
The clinical signs of CKD are non-specific, so diagnosis is based on collection of blood and urine samples. There are two substances in the blood - urea and creatinine - that are normally analysed, as they are excreted by the kidneys and so will rise in CKD. However, there are other conditions which can also cause these to rise, so a urine sample is usually analysed at the same time. In CKD the urine is more dilute than it should be.
HOW IS CHRONIC KIDNEY DISEASE MANAGED?
Some cats may require initial intravenous fluids (a drip) to correct dehydration and electrolyte abnormalities. Once stable, treatment is aimed at supporting renal function and minimising complications of kidney failure. The main method of treatment is dietary modification. CKD cannot be reversed, and in most cases it will progress over time despite appropriate therapy.
Optimal management usually requires repeat investigations at regular intervals (including blood pressure assessment, blood and urine tests) to identify treatable complications as they arise e.g. anaemia, low potassium, high phosphate, urinary infection and hypertension.
WHY IS DIETARY MANAGEMENT IMPORTANT?
Dietary management is crucial for cats with CKD and there are three main reasons for this:
- Water intake - cats with CKD are likely to become dehydrated as their kidneys are less able to concentrate the urine. Maintaining adequate water intake is therefore very important. Where possible, cats with CKD should be fed a wet diet, as they generally obtain much of their water intake from their food.
- Protein content - renal diets have a low protein content. Many of the toxic products that accumulate in the blood in renal failure are a result of protein breakdown, and feeding a low protein diet will help to minimise this. However, protein restriction must be performed with care, as too little protein can lead to excessive weight loss, so it is best to use commercial (rather than home-made) diets.
- Phosphate content - restricting phosphate content appears to be quite beneficial in protecting the kidneys from further damage. If a cat is not keen to eat a special renal diet, it is possible to add 'phosphate binders' to the diet to reduce the amount of phosphate that is absorbed - this should only be done under veterinary advice.
- Other dietary factors - renal diets are also often modified in other ways, for example the addition of fibre and some polyunsaturated fatty acids, which may have additional benefits in the management of CKD.
WHAT OTHER TREATMENTS ARE AVAILABLE?
There is a tendency for cats with CKD to become dehydrated, and this will have a significant adverse effect on kidney function. Hence there should always be fresh water available, and cats should be encouraged to drink by offering water from different bowls, using 'pet fountains', flavoured water (e.g. tuna or chicken) etc. Some cats (usually those with advanced CKD) may benefit from intermittent administration of fluids, either by intravenous drip, or given under the skin by injection.
With kidney disease, protein can be lost into the urine, and this is detected when the urine is tested. If significant protein loss is found, then we can use medication (ACE-inhibitors) to help reduce this loss. Current research suggests this medication can help to reduce ongoing damage to the kidneys.
Other treatments are generally aimed at specific complications that can arise:
- Potassium supplementation if levels are low, as this itself can worsen the renal disease, and lead to weakness. Where a deficiency is identified, tablets, gel or powder can be added to the diet.
- High blood pressure - cats with CKD that develop hypertension are then at risk of developing other problems such as retinal bleeding or detachment, or bleeding into the brain causing neurological signs, as well as a worsening of the kidney disease. It is therefore important to measure blood pressure and treat if it is high - this is usually straightforward in cats.
- Anaemia - if mild this may not be a major concern, but with advanced anaemia this can contribute to lethargy and weakness. Depending on the severity a number of different treatments are available, and your vet can discuss these with you if needed.
- Nausea and vomiting - these are more common in advanced CKD, and can significantly affect the quality of life and appetite of the cat. Anti-sickness drugs can be used if needed.
- Urinary tract infections - cats with CKD can be prone to these as their urine is more dilute than it should be, allowing bacteria to multiply - this can be treated with antibiotics.
WHAT IS THE PROGNOSIS IN CKD?
The disease is usually progressive over time, and will eventually lead to the need for euthanasia. However, the rate of progression varies between individuals, and appropriate treatment and support can both increase the quality of life and also slow down the progession of the disease.
WHERE CAN I FIND OUT MORE INFORMATION?
Feline Advisory Bureau and the Grove Lodge Vets website