Chronic Renal Failure

Renal failure (kidney failure) occurs when kidney function has
deteriorated to such a degree that the kidneys can no longer
perform their normal functions of excreting wastes, maintaining
water and electrolyte balance, and producing hormones. Renal
failure occurs in acute or chronic forms.

Acute renal failure is of recent onset and is potentially
reversible. In contrast, chronic renal failure has been present
for months to years at the time of diagnosis and is
irreversible. Dogs and cats with chronic renal failure cannot be
cured, but their clinical signs can often be managed
successfully.

Kidneys are composed of many small functional units called
nephrons (approximately 190,000 in cats and approximately
400,000 in dogs). Dogs, cats, and humans are normally born with
such an abundance of nephrons that signs of kidney failure do
not become apparent until more than two thirds of the nephrons
have been damaged. Because of this redundant kidney tissue, it
is possible to donate a kidney for transplantation and survive.
On the other hand, surplus nephrons make it difficult to detect
chronic kidney diseases until they are well advanced. As a
consequence, chronic kidney failure is often an insidious
condition that remains unrecognized until it is severe.

Because kidney disease is often quite advanced at the time of
initial diagnosis, the initiating cause of chronic renal failure
can rarely be established. Although chronic renal failure occurs
most often in older dogs and cats, renal failure is not simply a
result of aging.

The earliest signs of renal failure are typically thirst
(polydipsia) and increased urine volume (polyuria). These signs
result from inability of the diseased kidneys to form
concentrated urine. Other common early signs include weight
loss, poor haircoat, and an increasingly selective appetite.
Further decline in kidney function result in progressive
inability to excrete waste products, leading to retention of
toxic wastes in blood and tissues in the body. This is called
uremia (literally, urine in the blood).

Prominent clinical signs of uremia include loss of appetite,
vomiting, ulcers in the mouth, “uremic” (foul ammonia smelling)
breath, weakness, and lethargy. Other important effects of renal
failure include anemia (caused by inability of failing kidneys
to produce erythropoietin, the hormone responsible for making
red blood cells) and high blood pressure. Anemia worsens the
weakness, lethargy, and loss of appetite of dogs and cats with
chronic renal failure, and high blood pressure may cause sudden
blindness, strokelike signs (such as mental dullness, sudden
behavioral changes, coma, or seizures), or injury to the kidneys
and heart. Diagnosis of chronic renal failure is confirmed by
laboratory evaluation of your pet’s blood and urine. A urine
test can help determine whether the kidneys can form
concentrated urine and provide evidence of other urinary tract
problems such as urinary tract infections.

Blood tests used to evaluate kidney function include blood urea
nitrogen (BUN) and serum creatinine concentrations. Because the
kidneys excrete urea and creatinine, increases in urine and
creatinine concentrations in blood indicate decreased kidney
function. These tests are usually done together because they
provide different information. The serum creatinine
concentration is the more specific test for kidney function, and
treatment and other factors may influence the BUN.

In addition to evaluating kidney function, other tests may be
used to evaluate your pet for anemia, electrolyte and acid-base
abnormalities, nutrition, and hypertension. Ultrasound
examination and x-rays may also be used to evaluate kidney
disease.

Fortunately, most dogs and cats can be treated, providing a good
quality of life for months or years. Treatment for chronic renal
failure is tailored to the unique clinical requirements of each
pet but may include a special diet (e.g., limiting protein,
phosphorus, and salt intake); hydration therapy; and medications
designed to control clinical signs (such as poor appetite,
nausea and vomiting), acid-base and electrolyte disturbances,
anemia, and hypertension.

Consumption of excess protein may make some pets ill because the
waste products of protein metabolism are excreted by the kidneys
and are retained in renal failure. Dehydration (abnormal
depletion of body fluids) is a special threat to pets with renal
failure, and they may deteriorate if episodes of vomiting,
diarrhea, or inadequate water intake are not dealt with
promptly. Water should never be withheld from dogs and cats with
renal failure.

In humans, renal failure is most often managed by dialysis
(hemodialysis or peritoneal dialysis) or renal transplantation.
Chronic hemodialysis and peritoneal dialysis have thus far not
proved to be satisfactory options for dogs and cats with chronic
renal failure because they are expensive and fail to provide an
acceptable quality of life. Renal transplantation is an
expensive but potentially useful option for selected cats but
has not met with similar success in dogs. Renal transplantation
is best reserved for cats that can no longer be managed by
standard medical therapy.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.