What do my dog's kidneys do?
The kidneys have many functions. They principally act to remove waste products from the blood stream, regulate the levels of certain essential minerals such potassium and sodium, conserve water, and produce urine.
What is chronic renal failure? Is it the same as chronic kidney disease?
Many people think that ‘chronic kidney failure’ or ‘chronic renal failure’ means that the kidneys have stopped working and are not making urine. This is not the case. By definition, chronic renal failure (CRF), or chronic kidney disease (CKD) is the inability of the kidneys to efficiently filter the blood of waste products, not the inability to produce urine. Ironically, most dogs in kidney failure produce large quantities of urine, but the body's toxic wastes are not being effectively eliminated.
When do most cases of chronic kidney disease occur?
Since kidney tissue cannot regenerate if destroyed, the kidneys have a large amount of reserve capacity to perform their various functions. At least 2/3 of the kidneys must be dysfunctional before any clinical signs are seen.
In many cases, this means that the destruction has been occurring for months to years (chronic) before failure has become evident.
In dogs, chronic kidney disease is associated with aging, and in simple terms can be considered to be the 'wearing out' of the kidney tissues. The age of onset is often related to the size of the dog. For most small dogs, the early signs of kidney disease occur at about ten to fourteen years of age. However, large dogs have a shorter life span and may undergo kidney failure as early as seven years of age.
What are the clinical signs of chronic kidney disease?
When disease or advanced age causes the filtration process to become inefficient and ineffective, blood flow to the kidneys is increased in an attempt to increase filtration. The body must increase the amount of blood flowing through the kidneys since less and less of the toxins are being removed each time. This results in the production of more urine. To keep the dog from becoming dehydrated due to increased fluid loss in the urine, thirst and water consumption is increased.
Therefore, one of the earliest clinical signs of kidney failure is increased water consumption and urination, and is called compensated renal failure. After approximately 2/3 of the kidney tissue is destroyed, there is a rapid rise in waste products in the bloodstream and an apparent sudden onset of severe disease. The clinical signs of more advanced kidney failure include loss of appetite, lethargy, vomiting, diarrhea, and very bad breath. Occasionally, ulcers will be found in the mouth.
How is chronic kidney failure diagnosed?
There are two basic tests for kidney function: a complete urinalysis and a blood chemistry analysis.
A urinalysis is needed to evaluate kidney function. A low urine specific gravity (USpG) is the earliest indication of kidney failure. An increase in protein in the urine (proteinuria) also indicates decreased kidney function.
A blood biochemistry analysis assesses the function of various internal organs. Measuring the level of two waste products in the blood, namely blood urea nitrogen (BUN) and blood creatinine (CREA), indicates decreased kidney function. Tests to measure the blood levels of other substances such as albumin, globulin, potassium, sodium, phosphorus, and calcium, as well as the red and white blood cell counts are important in order to determine the extent of failure and the best course of treatment.
SDMA (a naturally occurring biological indicator for kidney function) can also be used to determine if early renal failure is occurring. SDMA concentrations increase above the normal reference interval well before serum creatinine becomes elevated. Whereas creatinine increases when about 2/3 of kidney function is compromised, the SDMA changes when approximately 50% dysfunction is present. This will help your veterinarian provide treatment for your dog at a much earlier stage in the disease.
"A urinalysis is needed to evaluate kidney function."
A dog in compensated chronic kidney failure with marginal kidney function may have normal levels of BUN and creatinine but will have a low urine specific gravity. If a major stress such as illness or surgery occurs, the kidneys may fail, sending the blood test values up quickly.
A dog diagnosed with low urine specific gravity as well as elevated BUN and CREA is said to be azotemic.
How will my veterinarian determine the degree kidney failure in my dog?
Your veterinarian may use the IRIS (The International Renal Interest Society) staging system. IRIS staging is based on serum creatinine levels, with sub-staging based on the presence of protein in the urine (as determined by a urine protein:creatinine ratio [UPC]) and measuring your dog’s blood pressure. By using this staging, your veterinarian has a better idea of how to proceed with treatment, monitor progress, and to estimate your pet’s prognosis.
Since chronic kidney disease is basically just a wearing out process, how is it treated?
The treatment of chronic kidney disease depends on the results of blood tests, and specific treatments are aimed at resolving specific abnormalities. In some cases, the kidneys are damaged beyond repair before diagnosis and medical treatment is ineffective. However, with early diagnosis and aggressive treatment, many dogs will live a normal lifestyle for many months or years.
"...with early diagnosis and aggressive treatment, many dogs will live a normal lifestyle"
Treatment usually occurs in two phases, first flushing the kidneys and removing the accumulated toxins from the blood, and then providing treatments to manage the disease and delay its progression.
What is involved in the first phase of treatment?
In the first phase, high doses of intravenous fluids are given to 'flush out' the kidneys and bloodstream. This flushing process is called diuresis and helps mildly damaged kidney cells to function again by removing the toxic metabolites and creating a healthier environment for healing.
If enough functional kidney cells remain, they may be able to adequately meet the body's needs for filtration and waste removal. Fluid therapy includes replacement of various electrolytes, especially potassium. Other important aspects of initial treatment include proper nutrition and medication to control nausea, vomiting, and diarrhea if present. Your dog will often begin to feel better soon after this stage of treatment is begun.
What can I expect from this first phase of treatment?
There are three possible outcomes from the first phase of treatment:
1. The kidneys will resume functioning and continue to function for a few weeks to a few years.
2. The kidneys will resume functioning during treatment but fail again as soon as treatment stops, usually within three to fourteen days.
3. Kidney function will not return.
Unfortunately, there are no reliable tests that will predict the outcome. Each case should be treated aggressively and monitored closely. Even dogs that have severe kidney failure may respond favorably to treatment and resume a normal quality of life after treatment.
If the first phase of treatment is successful, what happens next?
The second phase of treatment is to help keep the kidneys functioning as long and normally as possible. This is usually accomplished with one or more of the following, depending on your pet's condition:
A special diet - Nutrition is one of the cornerstones in the effective treatment of dogs with chronic kidney failure. The ideal diet for a dog in the advanced stages of kidney failure is lower in protein, low in phosphorus, and is not acidified. This type of diet helps reduce the amount of protein wastes or metabolic toxins that may make your pet feel sick and lethargic. In advanced kidney disease, a decreased protein diet will also decrease the workload on the kidneys. The most nutritionally appropriate diets are available from your veterinary clinic and common ones are Hill's Prescription Diet K/D, Purina Veterinary Diet NF, and Royal Canin Renal Support.
Nutritionists have developed commercial therapeutic diets that are designed for treating various stages of chronic kidney disease. Your veterinarian will recommend the most appropriate diet, containing the necessary quantity and quality of nutrients for your dog.
A phosphate binder - Phosphorus is removed from the body by the kidneys. Once the filtration process is impaired, phosphorous begins to accumulate in the blood. Elevated blood phosphorus levels also contribute to lethargy and poor appetite. Certain drugs (such as aluminum hydroxide, lanthanum, and calcium carbonate with chitosan) will bind excess phosphates in the intestinal tract so they are not absorbed into the bloodstream, resulting in lower blood levels of phosphorus.
"The second phase of treatment is to help keep the kidneys functioning as long and normally as possible"
Home fluid therapy - Once your dog is stabilized, you can give maintenance levels of fluids under the skin (subcutaneously) to your dog at home. This serves to prevent dehydration, helps continually flush toxins from the kidneys and provides additional levels of electrolytes. This is done from twice daily to once weekly, depending on the degree of your dog's kidney failure. Most dogs do best when they receive a small amount of fluids on a daily basis. Once the dog becomes stable, the frequency of treatment may be decreased. This may be more challenging with larger dogs as the volume of fluids may not be adequate to fully flush out their body though every bit helps. Although home fluid therapy might not sound like something you can do, you will be surprised at how easy the technique is and how well most dogs tolerate it. For detailed instructions on this procedure, see handout "Subcutaneous Fluid Administration in Dogs".
Therapy for protein in the urine (proteinuria) - Dogs with protein in the urine have increased risk of progression of CKD. Angiotensin converting enzyme inhibitors (blood pressure medications) will help to lower pressure in the kidneys, therefore lessening the degree of proteinuria. Drugs commonly used include benazepril and enalapril.
A drug to regulate the parathyroid gland and calcium levels - Calcium and phosphorus must remain at about a two-to-one (2:1) ratio in the blood. The increase in blood phosphorus level secondary to kidney failure stimulates the parathyroid gland to increase the blood calcium level by removing it from bones. This can be helpful for the sake of the normalizing calcium to phosphorus ratio, but it can make the bones brittle and easily broken. Calcitriol can be used to reduce the function of the parathyroid gland and to increase calcium absorption from the intestinal tract. This medication is needed if there is evidence of abnormal function of the parathyroid gland.
A drug to stimulate the bone marrow to produce new red blood cells - The kidneys produce a hormone (erythropoietin) that stimulates the bone marrow to make red blood cells. Therefore, many dogs in kidney failure will be unable to produce erythropoietin and have anemia or a low red blood cell count. Synthetic erythropoietin may stimulate the bone marrow to make red blood cells and correct the anemia in most dogs. Unfortunately for some dogs, the drug cannot be used long term because the immune system recognizes the drug as ’foreign’ and will make antibodies against it. A better option may be the alternative hormone darbepoetin which is less likely to cause those antibodies to form or at least not as quickly. This treatment may be recommended if your dog has persistent anemia.
How long can I expect my dog to live?
The prognosis is quite variable depending on the stage of kidney disease at time of diagnosis, your dog's response to the initial stage of treatment, and your ability to perform the follow-up care. Veterinarians encourage treatment in most situations because many dogs will respond well and maintain a good quality of life.
Treatment and follow-up care is relatively easy and inexpensive and extending the length and quality of life for their faithful companion represents the ultimate reward for many clients.