Kidney disease may be the most common ailment of cats over the age of nine years.  Kidneys are the organs in the body that are responsible for filtering out metabolic waste products from the blood, conserving water in the body, and producing urine.  A cat’s body is a wonderful machine, and even though it works best with two kidneys, it can perform well with just one kidney or 50% function.

Your veterinarian (or your physician) might use the term renal to describe things that have to do with the kidneys.  For example renal insufficiency means loss of kidney function.

There are many diseases that can affect the kidneys, but regardless of the cause, most renal diseases are treated similarly.  The prognosis for cats with kidney disease depends on whether the disease is acute or chronic.  Long standing problems tend to have less favorable outcomes.  Unlike other vital organs, such as the liver, the kidneys are not capable of regenerating themselves.

The signs associated with kidney disease are not necessarily unique and can include increased thirst, increased urination, weight loss, dehydration, dental disease, and vomiting.  Blood tests and urinalysis results will not indicate that kidney function is compromised until more than 50% function is lost.  In fact, they may not show abnormal results until about two thirds of function has been affected.

The most common parameters for evaluating kidney function are blood levels of BUN and creatinine, and urine specific gravity.  BUN stands for blood urea nitrogen, a breakdown product of protein metabolism.  Creatinine is another type of nitrogenous waste product.  Both build up to abnormal levels when the kidneys aren’t working.  Urine specific gravity relates to the concentrating ability of the kidneys.  Cats typically have very concentrated urine, meaning it has low water content.  In cats with kidney disease, the urine specific gravity drops because the urine becomes dilute and too much water leaves the body.

Cats with kidney disease tend to become dehydrated.  A skin turgor test is a simple procedure that cat owners can do at home to check on their cat’s hydration.  If neck skin is pinched up and does not fall back into place within a second or two, the cat is significantly dehydrated.  In this situation, injectable fluid supplementation is probably needed.

Pyelonephritis and glomerulonephritis are the terms used to describe infection and inflammation involving different cells within the kidneys.  Because the kidneys filter all of the body’s blood, any infectious agent in the blood is transported to the kidneys.

The clinical signs of pyelonephritis are the same as other types of kidney disease, but fever and pain on palpation of the kidneys may be present.  White blood cells can also be present in the urine.

Young adult cats are most often affected with glomerulonephritis, although it is not a common disease.  It can present itself in two ways:  nephrotic syndrome and renal failure.  In nephrotic syndrome cats develop swelling, fluid in their abdominal cavity, high levels of protein in their urine, increased blood cholesterol levels, decreased blood albumin levels, mild weight loss and loss of appetite.

Kidney infections are very serious, and are usually treated by giving intravenous antibiotics.  After initial treatment, oral antibiotics can be used, but three to six weeks of medication may be needed.  When pyelonephritis is suspected, a urine culture and antibiotic sensitivity should be started before treatment begins, and repeated after treatment to be that the infection has cleared.

There are genetic kidney diseases seen in several breeds of purebred cats.  The two most common types are renal amyloidosis in Abyssinians and Somalis, and polycystic kidney disease in Persians and Himalayans.  These diseases cannot be cured and are progressive.  Treatment focuses on keeping the cat comfortable and maintaining fluid and electrolyte balance.

There is no screening test for renal amyloidosis, but it is suspected in young to middle aged purebred cats who develop kidney disease of no other known cause.  A kidney biopsy can show the particular protein deposits that are the characteristic of this disease.

Polycystic kidney disease (PKD) is found in purebred cats and in related long haired cats.  This disease can be diagnosed by feeling lumpy, bumpy kidneys on palpation and by seeing the cysts on ultrasound.  There also is a DNA test that shows whether the gene responsible for the disease is present.  This test should be performed by all ethical breeders of at risk breeds to be sure they don’t breed any PKD positive cats.  The presence of cysts will not necessarily cause significant kidney disease, and some affected animals live normal lives.  Others develop kidney dysfunction at a young age as the cysts grow and destroy the normal kidney tissue.

In my next column, I will focus on Chronic Kidney Disease which is very common in senior cats.

Written by Dr. Wexler-Mitchell of The Cat Care Clinic in Orange, CA
Copyright © 2011 The Cat Care Clinic