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.

Causes

As one of the most common causes of death in the geriatric cat, CRF can occur as a result of:

  • Kidney inflammation
  • Congenital renal diseases
  • Renal lesions
  • Unresolved pyelonephritis (bacterial infection of the kidney)
  • Feline leukemia
  • Feline infectious peritonitis
  • Hypertension (high blood pressure)
  • Toxins
  • Chronic immune stimulation including chronic oral and skin infections, inflammatory bowel disease, pancreatitis, diabetes
  • Unknown causes

Signs

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) and polyuria (increased urination).  These are also the two most common signs of diabetes.

As CRF progresses, other physical signs include:

  • weight loss
  • dull coat
  • dehydration
  • lethargy
  • vomiting
  • muscle wasting
  • depression
  • mouth ulcers
  • halitosis
  • coma

Diagnosis and Testing

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.

Other tests to determine kidney function include x-ray of the kidneys, kidney ultrasound and biopsy.

Special Considerations for Diagnosing Diabetics

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.

This misdiagnosis results in delayed treatment and therefore faster progression of CRF as well as mismanagement of diabetes. If the owner is assessing diabetes control by measuring fluid intake and output only, the cat can be inappropriately overdosed with insulin.

Because the diabetic cat is prone to CRF as well as other illnesses, it is advisable for the cat to undergo periodic examinations including a comprehensive blood work panel and urinalysis. If at all possible, periodic blood pressure of the diabetic cat is also recommended as hypertension can results from poorly controlled diabetes, and untreated hypertension can lead to CRF.

Treatment

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.

Diet

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.

Low phosphorus foods for CRF can be found listed at the following pages:

For drinking water, distilled water is recommended because tap water and bottled water with added minerals can be hard on the kidneys.

Fluid Therapy

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.

Administering Subcutaneous Fluids To Your Cat is an excellent site for illustrating the technique of home administration of subcutaneous fluids. 

IV fluid therapy, usually given in the veterinary hospital, is often administered to cats with dangerously high renal values.  These cats will have severe symptoms and are gravely ill.  Once the cat has been stabilized, subcutaneous fluids will be continued at home.

Other CRF Treatments

Calcitriol

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.

Potassium supplementation

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.

A phosphate binder

(Alternagel, Alucaps) may be used to bind phosphates in the diet, reducing phosphorus intake and normalizing blood phosphorus levels.

Hypertension

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.

Epogen

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

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.

Gastrointestinal distress

To counteract gastric upset in the CRF cat, small amounts of Pepcid-AC can be given.

Constipation

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.

Special Considerations for Treating Diabetics

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.

The diet typically indicated for CRF cats can be contraindicated in the diabetic. Diabetes experts recommend feeding a high protein diet, which can significantly reduce blood glucose levels.  However, many high protein foods are also high in phosphorus, so for difficult to regulate diabetics, a decision must be made as to which diet to choose. A good compromise may be to offer a low phosphorus diet with the addition of a high quality protein source such as boiled chicken, turkey, liver, or eggs.

Questions for your vet

Ask your vet what he or she recommends concerning screening for CRF in the diabetic cat. Especially if your cat’s 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.

If your cat is diagnosed with CRF, ask your vet about his beliefs concerning diet and home administration of subcutaneous fluids. Discussing the other treatments for CRF would also be advisable.

If your vet does not have access to blood pressure monitoring equipment, see if he will refer you to a vet with this capability.

This page has been designed to give an overview of chronic renal failure in the diabetic cat. For more comprehensive information, please visit the sites listed below.

Resources

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
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This site is for information purposes only.  Please consult your veterinarian.