Renal disease is a general term for the dysfunction, impairment or failure of one or both kidneys. The kidneys are responsible for filtering nitrogenous and other waste products from circulation and excreting them in urine. The kidneys also produce a number of essential hormones and help regulate the concentrations of hydrogen, sodium, potassium, phosphate and other substances in bodily fluids. The kidneys are involved calcium metabolism, phosphorus production, blood pressure regulation and circulating red blood cell volume. Once a significant portion of functional kidney tissue has been destroyed, the dog becomes increasingly unable to filter and excrete waste products, causing them to build up to toxic levels in the blood.
Causes of Canine Kidney Disease
Canine kidney disorders can be classified into those that are chronic and those that are acute.
Chronic kidney disorders are caused by long-term insult to the kidneys which, over time, damages their ability to adequately concentrate urine and remove wastes from circulation. As kidney function deteriorates, the dog retains nitrogen, acids, ammonia and other toxic substances in its blood and tissues, causing a condition called uremia. Chronic kidney disease can be caused by trauma, congenital abnormalities (present at birth), chronic urinary tract obstruction, kidney infection (pyelonephritis), kidney stones (uroliths), cysts (polycystic kidney disease), exposure to renal toxins (nephrosis; can be caused by aspirin, butazolidin, ibuprofen and prolonged administration of certain antibiotics), lymphoma, nephritis (inflammation associated with infectious diseases such as hepatitis, ehrlichiosis, leptospirosis, Rocky Mountain spotted fever, systemic lupus erythematosus, chronic pancreatitis and Lyme Disease, among others), advancing age and a number of other disorders.
Acute kidney disease appears abruptly and can be caused by venomous snake or insect bites, complete obstruction of the urinary tract (tumor; urolith/calculi/stones), trauma, shock (insufficient blood flow to the kidneys), rupture of the urethra or bladder, bacterial or viral infection, congestive heart failure (inadequate blood flow to the kidneys), hypoadrenocorticism (Addison's disease), prolonged anesthesia and exposure to or ingestion of renal poisons (especially antifreeze, heavy metals, raisins, grapes, Easter lilies and rat bait [rodenticide containing cholecalciferol]). If appropriate treatment is provided quickly, it may be possible to prevent permanent kidney damage in dogs with the acute onset of kidney disease.
Prevention of Kidney Disease in Dogs
The best way to prevent chronic kidney disease is to have annual blood and urine tests to assess kidney function and overall health, especially in aging dogs. Owners also can manage the risk of kidney disease by feeding their dogs a high-quality, nutritionally balanced diet and providing free access to fresh water at all times. Antifreeze, human medications, household cleaners, pesticides, rodenticides, fertilizers, batteries and other potential renal toxins should be kept well out of reach of all companion animals.
One of the most troubling aspects of kidney disease is that affected dogs usually do not show clinical signs until their kidneys are severely damaged. Symptoms typically do not appear until roughly 75% of functional kidney tissue has been destroyed. The clinical signs of both acute and chronic kidney disease are largely nonspecific and seem to appear suddenly, even though the disease probably has been progressing for some time. Chronic renal disease cannot be cured, but it may be managed with medication, dietary modification and other supportive therapies.
Kidney disease is fairly common in domestic dogs, particularly as they advance in age. While a number of things can contribute to kidney disease, the symptoms tend to be nonspecific. Early diagnosis and intervention may help curb progressive kidney damage in acute cases. However, especially in chronic cases, one or both kidneys usually are severely and irreparably damaged by the time observable signs appear.
Symptoms of Canine Kidney Disease
The symptoms of kidney disease result from the body's attempt to compensate for the kidneys' diminishing ability to flush toxins out of circulation. Ultimately, with chronic disease, those attempts are unsuccessful. The symptoms of kidney disease include:
Increased thirst and water consumption (polydipsia; often dramatic)
Increased urine output (polyuria; often dramatic)
Inappropriate urination (in the house, car, elsewhere; "housetraining accidents")
Loss of appetite (anorexia; inappetence)
Disinterest in normal activities (apathy)
Bad breath (halitosis; ammonia-like smell)
Brownish discoloration of the tongue
Loose teeth ("rubber jaw")
Abdominal discomfort and pain
Swollen extremities (edema; ascites; fluid build-up)
Pot-bellied appearance of the abdomen (edema; ascites; fluid build-up)
Bleeding disorders (gastrointestinal hemorrhage; poor blood coagulation/clotting)
Poor hair coat and skin condition (dry; flaky)
Reluctance to exercise
Pale gums (mucous membrane pallor; usually mild)
Muscle wasting (atrophy)
Altered states of consciousness (disorientation; confusion)
As the kidneys deteriorate, the urine becomes less concentrated and lighter in color. Dogs with end-stage kidney failure develop high blood pressure, stop eating, make few if any attempts to urinate and produce little or no urine. They ultimately collapse, go into a coma and die. Unfortunately, owners usually cannot detect chronic kidney disease until the damage has become irreversible.
Dogs at Increased Risk
Kidney disease becomes more common with advancing age. Dogs that have suffered previous episodes of acute renal disease have an increased chance of developing chronic kidney disorders. Certain breeds are reported to have a hereditary or familial predisposition to developing kidney disease, including the Alaskan Malamute, Basenji, Beagle, Bedlington Terrier, Bernese Mountain Dog, Bull Terrier, Cairn Terrier, Chow Chow, Cocker Spaniel, Doberman Pinscher, Golden Retriever, Keeshond, Labrador Retriever, Lhasa Apso, Miniature Schnauzer, Newfoundland, Norwegian Elkhound, Pembroke Welsh Corgi, Rottweiler, Samoyed, Shar-Pei, Shih Tzu, Soft-Coated Wheaten Terrier and Standard Poodle.
Kidney disease in dogs can be reliably diagnosed through blood and urine tests. In some cases, ultrasonography is also used to assess the extent of the disease.
How Canine Kidney Disease is Diagnosed
Simple blood and urine tests are available to diagnose most cases of kidney dysfunction. The common blood tests are a complete blood count (CBC) and a serum biochemical profile. Dogs with kidney disease have elevated levels of blood urea nitrogen (BUN), creatinine, phosphorus, potassium and other electrolytes, caused by the kidneys' progressively deteriorating ability to filter waste products from blood and excrete them in urine.
The other main diagnostic tool for renal disease is a urinalysis. Veterinarians have chemical reagent test strips, instruments and other tools to help them evaluate a dog's urine. Urine can be sampled by the "free catch" method (caught mid-stream to reduce contamination), by urinary catheterization or by a technique called cystocentesis. Cystocentesis involves puncturing the abdominal and bladder walls with a sterile needle and aspirating an uncontaminated urine sample into a syringe. The sample is assessed for color, odor, viscosity/turbidity/cloudiness and the presence of blood, casts, stones, crystals, protein, bacteria, glucose and other sediments and substances.
The veterinarian will also determine the urine's specific gravity. "Specific gravity" is the weight of a substance compared with the weight of an equal amount of some other substance taken as a standard. For liquids, the standard is water. One of the key functions of healthy kidneys is to concentrate urine by filtering circulating waste products into it. Normal canine urine has a specific weight when compared with an equal amount of water. Urine that is abnormally dilute (low specific gravity) is highly suggestive of kidney disease.
Many veterinarians recommend an abdominal ultrasound to visualize the physical structure of the kidneys. This can help determine whether one or both kidneys are affected and can identify masses or other anatomical abnormalities. Abdominal radiographs (X-rays) may be taken to identify kidney enlargement (renomegaly). An electrocardiogram (ECG) can be used to assess heart function, which often is adversely affected by the elevated blood potassium levels that accompany renal disease. Specific tests for ethylene glycol are available for cases of suspected antifreeze toxicity; tests are available to detect leptospirosis and lyme disease, as well. Urine culture and sensitivity are highly recommended in dogs with chronic kidney disease, as they can help identify asymptomatic urinary tract infections which commonly occur in these patients. The urine protein-to-creatinine ratio, and the glomerular filtration rate, can both be measured. Finally, biopsies can be taken of one or both kidneys, either by surgical exploration or with the guidance of ultrasonography. Biopsies are extremely valuable to guide treatment decisions and disclose the extent of kidney damage.
Genetic screening tests for predisposition to familial kidney disease are reportedly under development for the Lhasa Apso, Shih Tzu and Soft-Coated Wheaten Terrier
The damage caused by acute kidney disease can often be treated and even reversed. Unfortunately, chronic kidney disease is incurable. The goals of treating kidney disease focus on improving the dog's quality of life, by relieving the symptoms of uremia and delaying the progression of renal failure.
Dogs with acute renal disease normally require hospitalization and prompt administration of intravenous fluids at carefully managed, above-maintenance levels, to restore hydration and promote urination. An indwelling urinary catheter may be inserted so that urine output can be quantified. If necessary, urine production can be enhanced by administration of certain drugs. If electrolyte or acid-base imbalances are present, the attending veterinarian can prescribe supplements to restore normal levels. Other medications are available to relieve abdominal discomfort and manage vomiting (emesis).
Dogs with chronic kidney disease usually also require hospitalization to address dehydration by administering appropriate intravenous fluids and to provide essential nutritional support. Many veterinarians recommend feeding a "renal diet" that is high in quality and low in sodium and phosphorus. Whether to feed a low-protein diet to dogs with chronic kidney disease is somewhat controversial. Some veterinarians believe that a high-protein diet, or a diet containing poor-quality protein sources, increases the nitrogen load on the liver and kidneys, while others believe that feeding a food with high biological protein values can actually help preserve or at least prolong kidney function. Because dogs with kidney disease lose their appetite and suffer dramatic weight loss, it is more important to maintain sufficient caloric intake than it is to manage the precise nutritional components of their diet. Appetite stimulants, as well as medications to reduce gastric acid and relieve vomiting, are available from a veterinarian. Other soothing products can be given to relieve gastric ulcers, which often accompany kidney disease. Phosphate-binding drugs may be prescribed to lower blood phosphorus levels, and sodium-bicarbonate or vitamin B supplements may be recommended in some cases. Over time, it may become necessary for the owner to administer subcutaneous fluids periodically, and perhaps daily in the very end-stage of disease.
Several forms of dialysis have been used to manage kidney disease in dogs by taking over much of the filtering responsibilities of the kidneys. Peritoneal dialysis involves injecting a special fluid into the abdominal cavity through a catheter. This fluid is designed to absorb toxins across tissue and vascular boundaries and is removed through the same catheter after a predetermined period of time. Peritoneal dialysis is particularly useful for acute kidney disease caused by poisoning.
Hemodialysis is a blood purification process in which the dog's anticoagulated blood is circulated through an artificial kidney. The blood is exposed to a special solution across a semi-permeable membrane that essentially filters out toxins and metabolic waste products. The procedure is only available at a handful of veterinary referral centers, and it is extremely expensive and time-consuming. Each hemodialysis session lasts 3 to 5 hours and must be performed up to 3 times a week. Like peritoneal dialysis, hemodialysis is best used to rest the kidneys after acute toxic events.
Kidney transplants have been performed in companion animals, primarily in cats but also in dogs. They are uncommon and costly, and are performed only at a few specialized veterinary hospitals. Issues surrounding canine kidney transplantation are similar to those in humans, including finding an appropriate donor and managing post-operative organ rejection. One method being used to identify potential donors is to test shelter dogs for tissue compatibility. Once a donor dog is found, one of its kidneys is removed and transplanted into the dog with kidney failure. Dogs, like people, can live a full, productive life with one functional kidney. The recipient dog's owner usually agrees in advance to adopt the donor dog and provide it with a loving home for the rest of its life.
The outlook for dogs with renal disease is highly variable and can range from days to years following diagnosis. Dogs with chronic kidney failure have a more guarded prognosis than do those with acute disease.