The kidneys are part of the urinary tract and serve the purpose of filtering waste from blood, which is later excreted as urine. Kidneys are responsible for maintaining electrolyte (salt), pH (acid-base) and water balance, regulation of blood pressure, and eliminating wastes. They are also responsible for producing hormones and enzymes such as renin, calcitriol, and erythropoietin.
Kidney (renal) failure occurs when the kidneys can no longer perform their normal functions of excreting wastes, maintaining water and electrolyte balance, and producing hormones.
Renal failure can be classified as acute or chronic. Acute renal failure appears suddenly and can be reversed depending on the amount of damage to the kidneys. In contrast, chronic renal failure is present for months or years and cannot be cured, but symptoms can be managed to help maintain a reasonable quality of life for the affected dog or cat.
Renal failure is notoriously difficult to diagnose until it has reached an advanced, chronic stage. The smallest functional parts of the kidneys, called nephrons, are usually so abundant in dogs, cats, and humans that signs of kidney disease don’t present themselves until more than two-thirds of the nephrons have been damaged. As a result, the initiating cause of chronic kidney failure can rarely be determined.
Whenever your pet is showing signs of a health issue, your first step is to contact your primary care veterinarian. If it is indicated that your pet may have kidney disease or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.
Because kidney disease is usually advanced by the time it is noticed, it is often hard to determine the cause. The most common cause of kidney disease in pets is age-associated change to the organs that results in progressive damage to the nephrons. This leads to the kidneys’ decreased ability to concentrate the urine, followed by azotemia (elevation of kidney values).
Congenital kidney disease is often recognized on initial lab work done prior to routine surgery (such as a spay or neuter), or during wellness checks. Other causes of kidney disease are congenital abnormalities, infectious disease(s), cancer, toxins, and proteinuria (excessive protein loss through the kidneys caused by the diseases glomerulonephritis or amyloidosis).
Ingested toxins that can affect kidney function and lead to kidney failure include ethylene glycol (antifreeze), non-steroidal anti-inflammatory drugs (acetaminophen and ibuprofen), grapes or raisins, certain plant types (including those in the lily family), and specific classes of prescription and chemotherapy drugs. These toxins generally result in a syndrome referred to as acute renal failure, which is addressed differently than chronic renal failure. However, exposure to smaller amounts of these substances can lead to kidney injury and result in chronic disease later in life.
Protein-losing nephropathy is a disease characterized by excessive loss of protein through the glomeruli, which are the larger functional units of the kidneys,. This is often associated with inflammation of the kidney, and your veterinarian will want to do a complete work-up if he or she suspects this disease. Amyloidosis is an extreme form of protein loss through the kidney caused by accumulation of the protein amyloid in the kidney’s glomeruli. This is known to affect certain breeds, including the Shar Pei dog and the Abyssinian cat.
Infectious causes of kidney disease include pyelonephritis (bacterial infections of the kidney), Leptospirosis, and Lyme disease. It is important to note that Leptospirosis can be prevented through vaccination, so discuss this option during your next vet visit to make sure your pet is protected. Any infectious disease can also lead to glomerulonephritis by causing systemic inflammation and immune complexes to build up in the glomeruli of the kidneys. Infectious diseases can cause either acute or chronic renal failure.
The earliest signs of renal failure are typically increased thirst (polydipsia) and increased urination (polyuria). These signs result from the inability of the diseased kidneys to concentrate the urine, which results in water leaving the body sooner than it should, making your pet thirsty and needing to urinate frequently.
Other common symptoms associated with kidney disease include weight loss, poor hair coat, and an increasingly selective appetite. Further kidney function decline results in progressive inability to excrete waste products in the urine, leading to retention of toxins in the blood and tissues of the body. This condition is called uremia, the signs of which include loss of appetite, vomiting, ulcers in the mouth, “uremic” (ammonia-smelling) breath, weakness, and lethargy.
Anemia, which is low red blood cell count, is another significant consequence of advanced renal failure. Anemia is caused by the inability of the failing kidneys to produce erythropoietin, the hormone responsible for making red blood cells. Symptoms include pronounced lethargy, weakness, and loss of appetite, as it will amplify these symptoms of your pet’s renal failure. Hypertension (elevated blood pressure) is often associated with renal failure, and is a serious symptom as it can cause sudden blindness from retinal detachment and can cause further kidney and heart damage.
It is important to catch your pet’s kidney disease as soon as possible in order to provide treatment before there is permanent damage to your pet’s organ systems. If you notice any of these changes in your pet, have him or her evaluated by a qualified veterinarian.
Once kidney disease is initially suspected, a thorough diagnostic work-up is necessary. This is important in order to identify any treatable conditions that will allow you and your veterinarian to agree on a treatment plan for your pet to slow progression of the disease. This may also lead to specific treatment for identified causes of the kidney injury and allow for reversal of some of that damage. Indicated tests include full lab work - a blood chemistry panel, complete blood count and urinalysis, urine protein levels, urine culture and sensitivity, blood pressure determination, abdominal ultrasound, and, possibly, infectious disease titers to determine if an infectious disease is the cause of your pet’s ailment.
Laboratory work that evaluates your pet’s blood and urine will be used to confirm and diagnose chronic renal failure. A urine test can help determine whether the kidneys can concentrate urine, as well as provide evidence of other urinary tract problems such as infections or excessive protein loss through the kidneys.
Blood tests used to evaluate kidney function include the blood urea nitrogen (BUN) and serum (bloodstream) creatinine concentration tests. Because the kidneys excrete urea and creatinine as waste, tests showing an increase in these values indicate that the kidneys are not eliminating these wastes, as they should be. These tests are usually done simultaneously because they provide different information. The serum creatinine concentration is the more specific test for kidney function, as other factors can influence the amount of BUN in the bloodstream.
In addition to evaluating kidney function, other tests may be used to evaluate your pet for anemia, electrolyte and acid-base imbalances, and calcium and phosphorus levels.
Ultrasound and radiographs (x-rays) may also be used to evaluate the kidneys for other diseases – such as cancer, polycystic kidney disease, and hydronephrosis - that may cause renal failure. These imaging techniques will be able to tell you and your vet if your pet has any structural abnormalities or masses.
Once a work-up has been completed, your vet can make recommendations to help slow the progression of kidney disease.
Your vet will tailor your pet’s treatment for chronic renal to its unique clinical requirements, but may include a special diet and one or more medications to slow the progression of renal failure. Your pet may also require additional treatments to adjust acid-base and electrolyte disturbances, correct anemia, control excessive acid production in the stomach, and regulate high blood pressure.
The most important and easiest therapy for your pet is a veterinarian-prescribed low quantity, high quality protein diet.
Based upon the initial diagnostics, your veterinarian can devise a treatment plan and have an understanding of how advanced your pet’s kidney disease is based upon your pet’s urine culture and sensitivity, electrolyte abnormalities, and if there are elevated phosphorous levels or acid-base imbalances. Each of these findings, once identified, is treatable.
In late stages of chronic kidney disease, anemia (low red blood cell count) can develop and your veterinarian may recommend certain prescription medications to stimulate the production of more red blood cells by the bone marrow. Intermittent monitoring of blood values will be required to identify emerging problems that may alter treatment or provide information regarding the stability or progression of the renal failure.
All patients with chronic kidney disease require periodic blood pressure monitoring. Hypertension (high blood pressure) is a common result of kidney disease and is addressed through prescription medications and careful monitoring of kidney values and blood pressure. Hypertension is often seen in conjunction with proteinuria. Luckily, drugs in the ACE inhibitor class can treat both conditions, and are usually the veterinarian’s first choice of drug.
Diets along with other regimens, such as low-dose aspirin and fatty acid supplementation, also aid in the therapy of glomerulonephritis. Research has indicated that addressing proteinuria and blood pressure are as important as dietary therapy in management of long-term chronic renal failure patients. It is important that you stay vigilant in keeping your pet healthy by maintaining veterinary appointments to continue assessing your pet’s condition.
Pets with choric kidney disease are in constant danger of dehydration, and may deteriorate quickly if episodes of vomiting, diarrhea, or inadequate water intake are not dealt with promptly. It is your job as your pet’s advocate to watch for vomiting and diarrhea, and treat prolonged episodes as an emergency situation.
Never withhold water from dogs and cats with chronic kidney disease. Your vet may recommend additional fluid therapy (either intravenous or subcutaneous fluids) on an intermittent basis in pets that can’t maintain adequate hydration on their own. With training, you can learn to administer subcutaneous fluids in your own home, especially if your pet is cooperative.
An expensive but potentially useful option for many cats is kidney transplantation because it is relatively easy to find a compatible donor. For dogs, though, it is a less viable option because of the difficulty in finding a compatible donor. Still, stringent requirements must be established and met before transplantation is recommended. Renal transplantation is available in only a small number of veterinary practices. Talk to your vet to find out if your pet may be a good candidate for a kidney transplant, and if there is a facility near you that offers this treatment.
Acute-on-chronic kidney disease is a crisis situation when the kidney values acutely rise and result in your pet feeling sick, becoming dehydrated, not eating or drinking, and possibly vomiting. This is an especially dangerous situation that you should be on the watch for if your pet has been diagnosed with kidney disease. Since the kidneys are unable to retain enough fluid and your pet is not able to take in adequate amounts of fluids to make up for these losses, severe dehydration ensues, which makes the crisis more severe. This situation is managed through hospitalization for diuresis (aggressive intravenous fluid therapy), anti-nausea medication, and other therapy based upon diagnostics. Once discharged from the hospital, it is frequently recommended that these patients receive subcutaneous fluids (fluids administered under the skin) at home.
The Prognosis for kidney disease is variable and depends on the stage at which medical intervention begins. This is one reason it is so important that you take your pet to be evaluated as soon as you suspect he or she is developing symptoms. With any disease, early intervention is ideal; however, not always possible. It is recommended that pets have lab work done at least on a yearly basis to identify kidney disease - as well as other endocrine and metabolic conditions - as early as possible.
Fortunately, most dogs and cats that undergo treatment can maintain a good quality of life. Survival time in cats with chronic renal failure is typically longer than that of dogs. Though in humans renal failure is often managed with dialysis or renal transplantation, chronic hemodialysis has not proved to be a satisfactory option for dogs and cats because of the expense and the small size of many of our pets. With careful monitoring and by addressing the treatable conditions, many patients can live happily for years with kidney disease.