What do kidneys do?
The kidneys’ main functions are to remove waste from the blood stream, conserve water, produce urine, and regulate the levels of certain essential minerals such as potassium and sodium.
What is chronic kidney disease?
Chronic kidney disease (CKD) is the inability of the kidneys to efficiently filter the blood of waste products. The kidneys have a large amount of spare capacity to perform their various functions, so at least two-thirds (67% to 70%) of the kidneys must be dysfunctional before any clinical signs are seen. In many cases, kidney damage has occurred over several months or years (chronic) before the disease is evident.
In dogs, chronic kidney disease is associated with aging. For most small dogs, the early signs of kidney disease occur around 10 to 14 years of age, while large dogs may undergo kidney failure as early as seven years of age.
What are the clinical signs of CKD?
The earliest clinical signs of CKD in dogs are increased water consumption and urination. In the initial stages of kidney failure, the kidneys produce a larger amount of more diluted urine to cope with their inability to efficiently remove waste products. Dogs drink more to compensate for increased water loss. This stage is known as compensated kidney disease.
After approximately two-thirds of the kidney tissues fail, the amount of waste in the bloodstream increases quickly and severe disease seems to begin suddenly. In more advanced stages of CKD, signs include:
- Poor appetite
- Lethargy
- Vomiting
- Diarrhea
- Pale gums due to anemia
- Bad breath
- Ulcers in the mouth
What causes chronic kidney disease?
CKD is the end stage of various disease processes. It is most often associated with aging and can be seen as the kidneys simply “wearing out.” Diseases and conditions that can eventually lead to CKD include:
- Congenital malformations of the kidneys (problems that the dog is born with)
- Pyelonephritis (bacterial kidney infections)
- Glomerulonephritis (inflammation and damage to the kidney's filtration membrane)
- Neoplasia (tumors of the kidney), most commonly adenocarcinoma and lymphosarcoma
- Amyloidosis (build-up of an unusual protein in the kidney that prevents it from functioning normally)
- Various infectious causes, such as Lyme disease and leptospirosis
- Kidney stones or ureteral stones
How is CKD diagnosed?
Several blood and urine tests are needed to diagnose kidney disease:
- Urinalysis is required to evaluate kidney function.
- Urine specific gravity (USpG) is a test of urine concentration. A low USpG means the urine is diluted (watery), which is the earliest sign of kidney disease.
- Increased protein in the urine (proteinuria) also indicates decreased kidney function.
- Cystatin B is a new test done on urine that may detect kidney damage before other tests. It may be useful in cases of suspected early or acute kidney injury.
- Blood biochemistry analysis assesses the function of various internal organs. Increased amounts of waste products in the blood indicate decreased kidney function. Products measured include:
- Blood urea nitrogen (BUN)
- Blood creatinine (CREAT)
- Symmetric dimethylarginine (SDMA)
- Red and white blood cell counts help determine the extent of kidney failure and the best course of treatment.
- Other tests measure the blood levels of substances such as albumin, globulin, potassium, sodium, phosphorus, and calcium.
A dog with compensated chronic kidney failure with marginal kidney function may have normal levels of BUN and creatinine, with high normal to slightly elevated SDMA, and a low urine-specific gravity. If a major stress occurs, such as illness or surgery, the kidneys may fail quickly, increasing the blood test values. A dog diagnosed with low urine-specific gravity as well as elevated SDMA, BUN and CREAT is said to be azotemic.
How will my veterinarian determine the degree of kidney failure in my dog?
Your veterinarian may use the International Renal Interest Society (IRIS) staging system to assess your dog’s kidney disease. This system is based on blood creatinine levels, urine protein levels (measured with a urine protein:creatinine ratio, or UPC), and blood pressure. Staging helps your veterinarian choose the best treatment plan, monitor your dog’s condition, and estimate prognosis.
How is CKD treated?
CKD treatment depends on the stage of kidney disease as determined by blood and urine testing as well as blood pressure assessment. Treatments aim to resolve specific abnormalities and slow disease progression. Many dogs with CKD can maintain a good quality of life for months or years with appropriate treatment. Your veterinarian will work with you to determine the best treatment for your dog.
- Therapeutic diets. Restricted protein and low phosphorus diets help reduce waste products in the bloodstream and decrease the workload on the kidneys. Therapeutic diets are available from your veterinary practice, including Hill’s k/d, Royal Canin Renal Support, and Purina NF. Your veterinarian will recommend the most appropriate diet for your dog.
- Phosphate binders. Dogs with kidney disease may develop elevated blood phosphorus levels, which can contribute to poor appetite and lethargy. Oral phosphate binders, such as aluminum hydroxide, lanthanum carbonate and calcium carbonate with chitosan, help reduce phosphorus absorption from the intestinal tract.
- Anti-nauseant medications, antacids, and appetite stimulants. These medications may help dogs experiencing nausea, vomiting, diarrhea, or poor appetite. Anti-nauseants include maropitant (Cerenia®), antacids include omeprazole, appetite stimulants include capromorelin (Entyce®).
- Blood-pressure lowering drugs. Many dogs with CKD develop high blood pressure, which can further damage the kidneys. Blood pressure medications may be prescribed as part of treatment.
- Medication to reduce proteinuria. Dogs with protein in the urine (proteinuria) are at increased risk for CKD progression. Medications such as benazepril (Fortekor®) or telmisartan help reduce protein loss and may also help manage high blood pressure.
- Calcitriol therapy. Kidney disease can disrupt calcium and phosphorus balance, which may affect bone strength and parathyroid gland function. Calcitriol may be prescribed in some dogs to help regulate these mineral imbalances.
- Hormone replacement for anemia. The kidneys normally produce erythropoietin, a hormone that stimulates red blood cell production. Some dogs with CKD develop anemia and may benefit from treatment with darbepoetin.
- Subcutaneous (SQ) fluids. Some dogs benefit from fluid therapy given under the skin at home to help maintain hydration and flush out toxic waste products that accumulate in pets with kidney disease.
- Intravenous (IV) fluids. In advanced stages of kidney disease, high doses of IV fluids may be given to “flush out” the kidneys and bloodstream. This process, called diuresis, may help improve kidney function by removing accumulated toxins.
What is the prognosis for a cat with CKD?
The prognosis is variable, depending on a few factors: the stage of kidney disease at the 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 respond well and maintain a good quality of life.