Chronic renal failure (CRF) is a progressive disease involving long-term insult to the kidneys which, over time, damages their ability to concentrate urine and remove nitrogenous waste products from the blood. The primary waste product that builds up with kidney failure is blood urea nitrogen, or "BUN." After many months or even years, the increase in circulating toxins ultimately causes signs of uremic poisoning. Unfortunately, the symptoms of chronic renal failure usually are not apparent until the dog's kidneys are severely and irreversibly damaged. Chronic renal failure sometimes can be managed, but it cannot be cured.
Causes of Canine Chronic Renal Failure
Why dogs develop chronic renal failure is not known. It may be that with advancing age, the kidneys simply wear out. Genetics appear to be a factor as well, with a predisposition for familial inheritance reported in certain breeds. Other contributing factors include exposure to toxins, congenital kidney disorders, prior episodes of acute renal failure, chronic urinary tract obstruction or infection, nephrotoxic drugs (drugs toxic to the kidneys), polycystic kidney disease, lymphoma, diabetes mellitus and a number of other kidney-specific disorders.
Preventing Chronic Renal Failure
Most cases of chronic renal failure are not preventable. Dogs diagnosed with CRF and those with a family history of the disease should not be bred. Companion dogs – especially those over 7 years of age -- should receive an annual veterinary examination with blood and urine screening to monitor kidney function and the health of other vital organs. Early diagnosis of CRF and good supportive care can delay progression of the disease in some cases.
The prognosis for dogs with CRF is highly variable and difficult to predict; life expectancy can range from days to years after diagnosis. Once a dog is in chronic renal failure, a veterinarian is in the best position to discuss the course of disease and potential management options with the owner. Regardless of treatment protocols, chronic renal failure almost always worsens with time and ultimately is terminal.
Chronic renal failure (CRF) can be present without obvious symptoms for a very long time. When kidney disease is asymptomatic, it usually is called renal "insufficiency," rather than renal "failure". Unfortunately, once overt signs appear, the kidneys probably have lost over 75% of their ability to perform their normal functions of filtering toxins from the blood, excreting the end-products of metabolism in the urine and regulating the concentrations of hydrogen, sodium, potassium, phosphate and other essential electrolytes in bodily fluids.
Symptoms of Chronic Renal Failure
The symptoms of chronic renal failure are largely a result of the body's attempt to compensate for the kidneys' inability to flush toxins and other waste products out of the body. Among the first changes noticed by owners of dogs with CRF are excessive thirst marked by increased water intake and excretion of an unusually large volume of urine.
Symptoms of chronic renal failure can include one or more of the following:
Increased water intake (polydipsia)
Increased urine output (polyuria)
Loss of appetite (anorexia; inappetence)
Inappropriate urination (especially at night; nocturia)
Bad breath (halitosis; ammonia-like odor)
Discolored, brownish tongue surface
Bleeding problems (abnormal blood clotting; prolonged clotting times)
Changes in cognition or mental state
Oral ulceration (sores in the mouth and on the gums)
Loose teeth ("rubber jaw")
Poor haircoat (dry, disheveled, unkempt)
Poor body condition (loss of muscle tone, underweight)
Pale gums and other mucous membranes (pallor)
Acute onset blindness (from hypertension)
Seizures, tremors, shivering, shaking (late in disease)
Coma (end-stage disease)
Polyuria and polydipsia (also called "PU/PD") are very commonly associated with a number of disorders and, without more, are not diagnostic of CRF. However, excess water intake and urine output almost always accompany chronic renal failure when it is present. The bad breath and oral ulceration are caused by the build-up of toxic waste products in the blood. In severe cases, dogs with CRF may develop high blood pressure (hypertension), with the adverse effects associated with that condition.
Dogs At Increased Risk
Chronic renal failure is more common in older dogs, because it is normal for kidney function to worsen with age. However, dogs of any age can be affected. Certain breeds seem to have a familial hereditary predisposition to developing early-onset CRF, including the Basenji, Beagle, Bedlington Terrier, Bernese Mountain Dog, Bull Terrier, Cairn Terrier, Chow Chow, Cocker Spaniel, Doberman Pinscher, German Shepherd, Golden Retriever, Keeshond, Lhasa Apso, Miniature Schnauzer, Newfoundland, Norwegian Elkhound, Pembroke Welsh Corgi, Rottweiler, Samoyed, Shar-Pei, Shih Tzu, Soft-Coated Wheaten Terrier and Standard Poodle. Dogs with a history of acute renal failure episodes are more likely to develop chronic renal failure, as are dogs that have had kidney stones (nephroliths; uroliths) or other types of kidney disease.
Chronic renal failure (CRF) can be tricky to diagnose, because many of the signs of this disease are the same as those caused by other diseases or disorders. However, given time and a willing owner, veterinarians have the skills and the tools to arrive at a definitive diagnosis.
How Chronic Renal Failure is Diagnosed
Dogs with CRF that is severe enough to cause symptoms usually arrive at the veterinary clinic weak, lethargic, depressed, underweight and disheveled, with a history of vomiting, stumbling, diarrhea or constipation, bad breath and dehydration despite abnormally high water intake and urine output. In addition to a thorough physical examination, the initial diagnostic database usually includes a complete blood count, a serum biochemistry profile and a urinalysis. The results of these tests may reveal anemia, elevated blood urea nitrogen, elevated blood creatinine levels, abnormal urine specific gravity and/or urinary tract infection. Direct or indirect blood pressure testing may reveal hypertension, and abdominal ultrasounds and radiographs may identify abnormal kidney tissue or structure, cysts, tumors, obstructions or other disorders.
If the initial diagnostics suggest CRF, more advanced tests can be conducted to either confirm or rule out that disease. These include a urine protein-to-creatinine ratio, urine culture and sensitivity, urine sediment examination, measurement of the glomerular filtration rate and/or a fine needle aspirate or biopsy of kidney tissue. Your veterinarian can describe these procedures to you in greater detail if they become pertinent to your dog.
Urinary tract infections (UTIs) are common in dogs with kidney disease. Resolution of the UTI may help improve kidney function in certain cases of chronic renal failure.
Chronic renal failure can be present for a long, long time before a dog shows any symptoms of illness. Unfortunately, by the time an owner suspects that something is wrong, enough kidney tissue usually has been damaged to make the condition irreversible. Nevertheless, there are a number of management techniques and supportive treatments that may help delay progression of renal failure and enhance the dog's quality of life.
Treatment Options for Chronic Renal Failure
The goals of treating chronic renal failure are to alleviate the symptoms of uremia, delay progression of disease and improve and prolong the dog's overall comfort and quality of life. It is critical to flush circulating waste products from a dog in renal failure. Most decompensated dogs will not tolerate oral fluids or medications. Dogs showing severe uremic signs (dehydration, anorexia, vomiting) usually will be hospitalized so that the medical team can start immediate, aggressive intravenous fluid and electrolyte therapy. After dehydration has been corrected and the dog's electrolytes have been restored to their proper balance, fluids can be given under the skin (subcutaneously) rather than directly into a vein. Most owners can be taught to give subcutaneous fluids to their dogs at home without much difficulty. In late stages of CRF, the dog may need subcutaneous fluids daily to remain comfortable. The veterinarian may prescribe various supplements to replace vitamin B, correct acid-base imbalances and reduce circulating levels of phosphorus, as well.
Dietary changes can be quite helpful if customized to the individual dog. Protein is usually poorly metabolized by dogs with chronic renal failure, and circulating phosphorus and sodium (salt) tend to accumulate. Most renal diets have significantly reduced protein, phosphorus and sodium levels when compared with normal maintenance diets. Supplementation with omega-3 fatty acids may be beneficial, as well. Some dogs resist dietary changes, and it may quickly become more important for a sick dog to receive adequate calories than it is for him to receive a perfectly balanced diet. When a dog refuses to eat and starts losing weight, it is increasingly difficult for his body to combat disease. A highly palatable, high calorie diet may be best for a dog in chronic renal failure, at least in the short term, until the effects of the disease can be controlled. Of course, free access to fresh water is always important, but it is critical for a dog with kidney disease. The dog must be able to drink enough water to compensate for its increased urine output in order to prevent severe and debilitating dehydration.
If vomiting and ulceration are involved, a number of prescription and over-the-counter medications are available to decrease gastric acidity, reduce nausea and vomiting and soothe the stomach lining. A veterinarian can also recommend drugs to help control hypertension and anemia, if those are present. Some medications are known to cause renal (kidney) damage and obviously should not be used in dogs with renal failure.
Kidney transplants are available at only a handful of veterinary referral hospitals, but they are gradually becoming more common. Donor dogs are usually found in animal shelters and, if there is a tissue match, that dog donates one kidney to the recipient dog, and the owners of the recipient adopt the donor and provide a loving home for the rest of its life. Kidney transplants are very expensive and require long-term administration of drugs post-transplant to minimize the chance of organ rejection. Kidney transplants are uncommonly performed in companion dogs.
Kidney dialysis is another potential therapy. It is only available at a few veterinary teaching hospitals and highly specialized private referral centers. Hemodialysis involves routing the dog's blood through special catheters into a machine that is designed to take on the filtering functions of normal kidneys to remove circulating toxic waste products. The procedure lasts 3 to 4 hours and must be done several times a week. Dialysis is extremely expensive and is rarely used for chronic cases of renal failure in dogs.
If treatment and management attempts do not improve renal function and relieve the dog's extreme discomfort, euthanasia should be considered.
The prognosis for dogs with CRF is difficult to predict and can range from days to years. When a dog is diagnosed with chronic renal failure, its veterinarian is in the best position to discuss the course of the disease and treatment options with the owner. However, since the CRF is always progressive and incurable, the prognosis inevitably is guarded to poor. The focus of management should be on maintaining the best quality of life for the animal as long as possible.