Chronic kidney disease in cats can be treated successfully and many patients can look forward to months or often years of quality life
‘Chronic kidney disease’ is a term used to refer to cats with kidney insufficiency or failure. ‘Chronic’ simply means long term. ‘Insufficiency’ or ‘failure’ means that the kidneys are no longer able to adequately perform their normal tasks. ‘Chronic kidney failure’ refers to the situation where the kidneys have not been able to perform one or more of their normal tasks adequately for a period of time (months to even years). Because the word ‘failure’ evokes such a sense of doom, we often opt for the term ‘chronic renal insufficiency’ or ‘chronic kidney disease’ instead, as many cases can be treated successfully and can look forward to months or often years of quality life.
What do the kidneys do?
The kidneys perform many functions in the body, including:
- helping to maintain fluid balance in the body
- producing certain hormones which stimulate red blood cell production and activate Vitamin D
- regulating blood pressure
- regulating electrolyte balance
- excreting waste products in the urine. Blood is constantly filtered through the kidneys to remove the toxic waste products of the body’s metabolism. Urine is produced in this process.
- concentrating the urine by returning water to the body, preventing dehydration
Fortunately, there is considerable ‘reserve capacity’ in the kidneys. It is well recognised that in healthy animals and humans, it is possible to remove one kidney completely without any adverse consequences due to the capacity of the other kidney to take over normal function. In fact, two thirds to three quarters of the total functioning kidney tissue (of both kidneys) has to be lost before clinical signs of chronic kidney disease develop.
The kidneys perform a number of functions in the body
How common is chronic kidney disease in cats?
Chronic kidney disease can affect any cat, of any age, any sex, and any breed. It is most commonly seen in middle to old-aged cats (those over 7 years of age), and it becomes increasingly more common with advancing age. It has been estimated that around 20-50% of cats over 15 years of age will have some degree of chronic kidney disease and it is seen more frequently in cats than in dogs.
What causes chronic kidney disease?
Most cases of chronic kidney disease are considered ‘idiopathic’ (i.e. they have an unknown underlying cause). However, some causes are well known and recognised, including:
- Polycystic Kidney Disease (an inherited disease in Persians/Persian lines where cysts replace normal kidney tissue)
- infections (also called ‘pyelonephritis’, from infection from the bladder or bacteria from blood stream, or the disease Feline Infectious Peritonitis)
- toxins (e.g. antifreeze, certain drugs)
- tumours (e.g. kidney lymphoma)
Other conditions can also gradually affect the kidneys from birth (‘congenital’ defects). Trauma, hypokalaemia (low blood potassium), and hypercalcaemia (high blood calcium) can also be contributory causes of chronic kidney disease in cats.
Intensive research is still on-going in attempt to uncover the underlying cause(s) of most cases of this disease.
If an underlying cause can be identified, this is often treated in an attempt to slow the progression of ongoing and irreversible damage to the kidneys. In most cases however, treatment is usually directed at management of the disease and the complications which arise from it.
What are the clinical signs of chronic kidney disease in cats?
‘Azotemia’ is a condition where toxins have built up in the bloodstream and can be detected on blood tests. The term ‘uraemia’ means that the patient is experiencing symptoms of poisoning from the build-up of these products in the blood stream.
Many other signs of chronic kidney disease are considered vague and non-specific—some arise from the accumulation of toxins in the blood system whilst others arise as complications from the body trying to ‘stabilise’ the disease.
Clinical signs include:
- weight loss
- poor, unkempt hair coat
- excessive drinking
- excessive urination
- loss of appetite
- bad smelling breath (halitosis)
- high blood pressure
- (sometimes) calcification of soft tissue
How will my vet diagnose chronic kidney disease?
A diagnosis of chronic kidney disease is usually made by collecting both a blood and urine sample at the same time. There are two substances in the blood – urea and creatinine – which are commonly measured, as these are by-products of metabolism that are normally excreted by the kidneys. In chronic kidney disease, the blood concentration of these two products will increase to varying levels. There are other conditions which can also cause elevation of these substances (e.g. dehydration) and hence why a urine sample is usually assessed at the same time to assess the concentrating ability of the kidneys. Typically with chronic kidney disease, there will be increased urea and creatinine concentrations as well as poorly concentrated urine. The urine ‘specific gravity’ is a measurement of urine concentration.
Your vet will need to take blood and urine samples to diagnose chronic kidney disease
Furthermore, screening blood tests may also highlight important complications which may have developed as a result of chronic kidney disease such as hypokalaemia (low blood potassium), anaemia, and hyperphosphataemia (high blood phosphate). High blood pressure is a common complication of chronic kidney disease in cats and if uncontrolled, can worsen the kidney disease. Therefore, your vet will usually want to measure your cat’s blood pressure if there are any concerns about kidney disease. Depending on the case, your vet may want to perform additional tests such as total thyroid, urine culture (to rule out kidney infection), urine protein creatinine ratio to assess if there is significant protein loss in the urine which can contribute to the progression of kidney disease, and ultrasonography to rule out kidney or ureteral stones/cysts/masses.
If there are signs of kidney disease, your vet will attempt to ‘stage’ the disease on a scale of 1-4 (‘IRIS Staging’) depending on creatinine values, urine protein to creatinine value, and blood pressure measurements, in order to facilitate treatment and monitoring of the patient and progression of disease.
Early diagnosis of chronic kidney disease in cats
Because chronic kidney disease is such a common disease in cats, routine screening of all mature and older cats (over 7 years old) can assist with early diagnosis and intervention, which in turn, may slow down the progression of disease and prolong a good quality of life. Yearly or twice yearly routine veterinary examinations are extremely important in older cats. During these examinations, your vet will check a urine sample and record your cat’s body weight. A declining urine concentration or body weight may be early signs that chronic kidney disease is developing and that further investigations should be explored.
Regular check ups with your vet are important as your cat gets older
In the next article in this series, we look at how chronic kidney disease in cats can be treated.