Chronic Renal Failure
What is Chronic Renal Failure?
Chronic renal failure (CRF) occurs when 70% of kidney function is irreversibly destroyed. The kidneys consist of tiny units called nephrons, which are responsible for filtering out toxins and wastes from the blood. These toxins and wastes become concentrated in the urine and eliminated from the body. When the kidneys no longer have enough functioning nephrons to effectively rid the body of toxins, uremic poisoning results.
As one of the most common causes of death in the geriatric cat, CRF can occur as a result of:
The normally functioning kidney is able to rid the body of
toxins and wastes by storing them in the bladder as concentrated urine. However, the
failing kidney is unable to use a small amount of water for the toxins (concentrated
urine), and because of this failure in water conservation, more water is needed to flush
the toxins from the body. Consequently, the most common symptoms of CRF are polydipsia (increased drinking)
(increased urination). These are also the two most common signs of diabetes.
Diagnosis of CRF can be made by
a variety of methods. Physical examination findings of abnormally small or
large kidney(s) may initiate further testing of kidney function. Tests most
commonly utilized to assess kidney function include a urine specific gravity
test to determine how well the kidney is concentrating urine and blood work
to determine the levels of toxins in the blood. The two most significant
blood test results are the BUN (blood urea nitrogen) and the creatinine
levels. BUN is a protein metabolite and although lab values differ, the
approximate range is between 14-36 mg/dl (5-12.9 nmol/L) for healthy
kidneys. BUN is related more to diet, and if dehydration is present, will
show increased values. Creatinine is thought to be a more reliable indicator
of kidney function as it shows how well the kidneys are filtering out the
toxins and is less dependent on dietary factors and hydration status of the
cat. A normal range for creatinine value for the healthy kidney is 1.0-2.2
mg/dl (88.4-194.5 umol/L). Additional blood values used to diagnose renal
failure include phosphorus, potassium, calcium, and packed cell volume.
Because many of the same symptoms present in diabetes (e.g., PU/PD), are
also indicators of renal failure, CRF can be easily misdiagnosed as poorly
controlled diabetes. Elevated BUN and creatinine levels can also occur with
diabetes alone, so a diagnosis of CRF can be complicated.
CRF is a terminal illness. However, with specialized treatment, many CRF cats are able to live months to years before succumbing to the disease. The goal of treatment is to ease the work done by the kidneys and to prevent dehydration. Thus, management to slow the progression of the disease revolves around two mainstays of treatment, diet and fluid therapy, both of which are controversial.
Up until somewhat recently, the recommended diet was both low in protein and
phosphorus. However, there is new evidence suggesting that
the amount of protein is of less importance than the "quality" of
the protein source. Consequently, there are now two schools of thought, one
advocating the traditional low protein CRF foods and the other proposing a
higher or moderate protein diet using high quality proteins such as cooked
eggs, boiled liver, chicken, turkey, heart, etc. Many
vets do not recommend low protein/restricted protein diets for early, mild
or moderate disease. Restricted protein can be helpful in very severe CRF
because low protein reduces nitrogenous wastes, making it easier for the
kidney to do its job of filtering blood. However, both sides concur
with one aspect of the CRF diet: it must be low in phosphorus.
For drinking water, distilled water is recommended because tap water and bottled water with added minerals can be hard on the kidneys.
For most CRF cats at one stage or another, the mainstay of CRF treatment is
the administration of subcutaneous fluids which can slow the progression of
the disease by helping to keep the cat consistently hydrated. Fluid
therapy is given several times a week to several times daily depending on
the needs of the cat as determined by both renal values and overall
well-being. Caution, especially in cats with preexisting heart
disease, must be used with chronic administration of large amounts of
subcutaneous fluids because of the danger of inducing hypertension and/or
congestive heart failure.
Other CRF Treatments
There is increasing evidence that Calcitriol (vitamin D3) will delay progression of CRF by restoring calcium balance. Some experts are promoting the use of Calcitriol as long as a parathyroid hormone test determines that the cat is a candidate. If the calcium value multiplied by the phosphorus value exceeds 70, Calcitriol should not be given.
In CRF, potassium depletion is common. Many experts believe that potassium supplementation should be initiated before the potassium values reach the low end of the normal range. The most widely used potassium supplement is Tumil-K, available in tablet, powder and gel form. Potassium added to sub-q fluids is also an option but often causes discomfort to the cat during fluid administration.
(Alternagel, Alucaps) may be used to bind phosphates in the diet, reducing phosphorus intake and normalizing blood phosphorus levels.
This is a common result of CRF and must be treated so that strokes, heart disease and blindness are prevented. Currently, the drug of choice for hypertension in CRF cats is the calcium channel blocker amlodipine (Norvasc). The ace inhibitor, benazepril (Lotensin), is also gaining in popularity.
As CRF progresses, anemia results due to erythropoietin deficiency. Erythropoietin is made by the kidneys and is responsible for stimulating red blood cell production by the bone marrow. In chronic renal failure, erythropoietin is depleted causing anemia as reflected in a low packed cell volume value. Severe anemia is life threatening, as there are not enough red blood cells to deliver oxygen to the body tissues. Unfortunately, because the only erythropoietin drug available (Epogen) is human based, some cats develop antibodies to it causing the packed cell volume to fall even lower. Therefore, erythropoietin therapy is not initiated until the packed cell volume falls dangerously low (under 18-20).
Anorexia is common in the CRF cat. Appetite stimulants are often given to help promote appetence and help the cat maintain a stable weight. Drugs to stimulate appetite most commonly prescribed are Valium and Cyproheptadine. Valium (diazepam) has been know to cause serious liver and kidney damage in a small percentage of cats, so discuss the use of this drug with your veterinarian before administration.
To counteract gastric upset in the CRF cat, small amounts of Pepcid-AC can be given.
Many CRF and diabetic cats suffer from chronic constipation due to dehydration. Lactulose is often recommended as it can also theoretically aid the kidneys by helping to eliminate nitrogenous wastes through the digestive tract, thereby decreasing the load on the kidneys.
Diabetes and CRF are
intricately involved; the progression of one impacts the progression of the
other which makes control of each disease difficult to manage. CRF puts
immeasurable stress on the cat's body, making diabetes regulation
difficult, if not impossible. In turn, poorly controlled diabetes will
contribute to an accelerated progression of CRF, especially if hypertension
and urinary tract infections (UTIs) are present and inadequately addressed.
In the diabetic cat with or without CRF, it is important to have regular
screenings and treatment for any UTIs and periodic blood pressure testing if
at all possible.
Ask your vet what he or she recommends concerning screening for CRF in the diabetic cat.
Especially if your cats diabetes is well controlled and you still see signs of
PU/PD, have a blood panel done to rule out CRF (as well as other diseases such as
hyperthyroidism) as well as a urinalysis for urine specific gravity and to check for any
concurrent urinary tract infections.
There are several excellent resources on the Internet for CRF cats.
The information on the page was provided by Melissa, who has both CRF and CRF-diabetic cats. This page is in memory of her beloved Popcorn.
Updated January 2008
This site is for information purposes only. Please consult your veterinarian.