Chronic renal failure (CRF) is evidenced by a build-up of waste products and the inability of the kidneys to concentrate urine; it typically occurs when there is permanent irreversible damage to at least 75% of the kidney tissue. 

CRF is typically a disease of older cats and dogs and becomes more prevalent with old age. 

The actual function of the kidneys cannot be improved by treatment; the goals of treatment are to decrease the workload on the kidneys, decrease the adverse signs associated with CRF, and prevent progressive damage to the kidneys. 

What is Chronic Renal Failure?

• Normal kidneys excrete waste, maintain fluid and electrolytes, and produce hormones that stimulate red blood cell production, regulate calcium, and affect acid production in the stomach. 
• The kidneys have a large amount of reserve tissue and are still able to properly function when 50% of the tissue has been damaged (or one kidney has been removed).  In fact 66% of both kidneys must be destroyed before signs of increased thirst and urination become evident.
• Chronic renal failure (CRF) is evidenced by a build–up of waste products and the inability of the kidneys to concentrate urine; it typically occurs when there is permanent irreversible damage to at least 75 % of the kidney tissue.  
• A wide variety of diseases can cause the initial damage to the kidneys, however the exact cause of chronic renal failure in an individual animal cannot usually be determined and does not typically affect treatment. 

Clinical Signs

• CRF is typically a disease of older cats and dogs and becomes more prevalent with old age.  The average age of dogs with CRF is 7 years and the average age of cats with CRF is 9 years.   
• Approximately 9/1000 dogs and 16/1000 cats are affected, but these rates increase significantly with age. 
• Any breed can be affected, however some breeds such as Abyssinian and Persian cats, and Bull terriers, Cairn terriers, German shepherds, Samoyeds, and English cocker spaniels may have an inherited component to the disease.
• Typical signs of CRF
  • Increased urination--due to the kidneys’ inability to concentrate urine
  • Increased thirst--due to compensation of excessive water loss as result of increased urination
  • Dehydration--due to excessive loss of water in the urine
  • Weight loss--due to breakdown of tissues in the body in order to gain excess energy
  • Loss of appetite +/- vomiting--due to accumulation of toxins in the blood, ulcers in the stomach, and feelings of nausea
  • Unkempt haircoat--due to inadequate nutrients and dehydration
  • Ulcers in the mouth and bad breath--due to excessive accumulation of waste in the blood

Diagnosis

• CRF is usually diagnosed with bloodwork and urinalysis. 
• Bloodwork (chemistry panel) will typically show elevations in BUN and creatinine, protein breakdown products normally filtered by the kidneys, but incompletely filtered by the failing kidneys.  Higher levels of BUN and creatinine indicate more severe kidney failure. 
• Bloodwork (Complete Blood Count) will also likely show anemia (low red blood cell count) and many electrolyte and acid-base abnormalities. 
• Urinalysis will show a low urine concentration, known as low specific gravity.  Although the diagnosis is typically made based on bloodwork and urinalysis alone, abdominal ultrasound may also be indicated to rule out kidney stones or infectious causes of renal failure. 
• Occasionally in complicated cases, kidney biopsies may be needed to diagnose CRF.  It is also important to check blood pressure as about 60% of the animals with CRF have high blood pressure (hypertension).

Treatment

• The actual function of the kidneys cannot be improved by treatment; the goals of treatment are to decrease the workload on the kidneys, decrease the adverse signs associated with CRF, and prevent progressive damage to the kidneys. 
• Ill (vomiting and not eating) animals that present with CRF need to be hospitalized and given large amounts of IV fluids as well as IV medications to control vomiting and acid production. 
• Animals (especially cats) that will not eat may need a feeding tube to ensure adequate nutrition.  While in the hospital, the levels of BUN and creatinine need to be monitored daily. 
• Once they have decreased significantly (although remaining elevated) further treatment may be continued at home. 
• Animals with CRF able to be stabilized may be eligible candidates to undergo a surgical kidney transplant from a donor animal.

Home Care

• The diet should be changed to have low salt, low phosphorus, high quality protein, and vitamin supplementation. 
• Prescription diets such as Eukanuba early or late-stage renal, Hills k/d, or Purina NF fill these criteria. 
• Unlimited access to plenty of water is important for the animals to maintain hydration.  As the disease progresses, some animals may also need additional fluids administered under their skin at home on a daily basis. 
• Many animals will need to be given oral medications at home. 
• Stress to the animals should be avoided to help decrease protein breakdown in the body. 
• Bloodwork and urine will need to be re-checked regularly to monitor the progression of the disease. 

Potential Complications

• The kidneys are one of the body’s main pathways for filtering medications and anesthesia.  Animals with CRF may have decreased ability to tolerate medications and some medications are toxic to the already weak kidneys, so veterinarians need to be advised that a pet is in CRF before any medications or anesthesia is administered. 
• Pets with CRF typically have suppressed immune systems and may therefore require antibiotic therapy more often than a normal animal. 
• Some of the other complications of CRF are stomach ulcers, high blood pressure (and if uncontrolled sudden blindness), anemia, calcification of body tissues, fluid accumulation in the abdomen, heart problems, muscle weakness, and neurologic dysfunction.  
• Animals receiving kidney transplants may reject the transplant and require additional hospitalization and therapies.

Prognosis

• Unless a successful kidney transplant is performed, CRF is ultimately fatal.  Nevertheless, many animals (especially cats) may live a relatively good quality of life for months and possibly years while being managed at home. 
• Some animals may experience acute episodes of worsening CRF, which may require hospitalization and additional therapy in order to improve kidney values in the short-term, however some animals will only steadily deteriorate over time and additional hospitalization may not be indicated. 
• As CRF progresses, quality of life deteriorates; animals with end-stage renal failure have a very poor quality of life and are often euthanized in order to avoid suffering.

References

1. Adams, L/G. and Osborne, C.A.  Renal Failure, Chronic.  In Tilley, L.P. and Smith, W.K. (Eds.)  The 5-minute Veterinary Consult: Canine and Feline, 3rd Ed.  Lippincott Williams &Wilkins: Philadelphia, 2004.
2. Grauer, G.F. Chapter 44: Renal Failure.  In Nelson, R.W. and Couto, C.G. (Eds.).  Small Animal Internal Medicine, 3rd Ed.  Mosby, Inc.: St. Louis, 2003.
3. Yin, S.A.  The Small Animal Veterinary Nerdbook, 2nd Ed.  CattleDog Publishing: Davis, CA, 1998.