How Kidneys Work
The kidneys are a pair of organs inside the abdomen or belly that are part of the urinary tract, also known as the urogenital system. Their job is to filter toxins, waste, and extra water from the blood. They do this by making urine, which gets transported to the bladder via tubes called ureters. Kidneys also help maintain the electrolyte balance within the body, make red blood cells, and control blood pressure. When the kidneys don’t work properly, numerous body systems can be affected, including the heart and brain.
Kidney disease is classified in a few ways. Treatment, outcome, and causes will differ a bit between each category. Most commonly, you will see kidney disease referred to as either acute kidney failure (AKA acute kidney injury/AKI, acute renal failure/ARF) or chronic kidney failure (AKA chronic kidney disease/CKD, chronic renal disease, chronic renal failure/CRF).
Chronic kidney failure cannot be reversed or cured. The kidneys will continue to worsen. Damage to the kidneys has been happening for more than 3 months (as opposed to acute failure, which occurs much more rapidly). Chronic kidney failure is the most common type of kidney disease in dogs, occurring in 0.5-1% of dogs.
Causes of chronic kidney failure include birth defects or congenital diseases, polycystic kidney disease, kidney cancer (i.e. renal neoplasia), kidney infections, elevated calcium (i.e. hypercalcemia), Fanconi syndrome, renal dysplasia, kidney stones (i.e. nephroliths or renoliths), blocked urine movement or flow (e.g. partial or treated urinary tract obstruction), immune system dysfunction, poor blood flow to the kidneys/ischemia, and certain medications (e.g. NSAIDs, some antibiotics). Acute kidney failure can also lead to chronic kidney failure. In many cases, the cause of chronic kidney failure is not known.
Chronic renal failure is slow to progress. At first, the kidneys try to make up for the damage by increasing the filtering ability of the healthy parts of the kidney. Over time, this causes damage to the healthy kidneys and they lose the ability to filter properly. Proteins such as albumin, which help control the amount of fluid in the blood and support other body functions, enter the urine. Excessive amounts of certain electrolytes (e.g. potassium) and water are also lost in the urine leading to chronic/constant dehydration and electrolyte-related issues (e.g. muscle weakness). Increased blood pressure (i.e. hypertension) may occur. Gastrointestinal issues such as ulcers are common because the kidneys can’t filter out toxins (e.g. uremia). Excess phosphorus is also normally removed by the kidneys but tends to build up with chronic kidney failure. This can lead to further kidney damage. The kidneys also make the hormone erythropoietin, which is in charge of stimulating red blood cell production. In chronic kidney failure, the kidneys don’t work well enough to make this hormone, so anemia (i.e. low red blood cells in the bloodstream) is also common.
Symptoms and Identification
Those in chronic kidney failure may not show any symptoms at first, or the symptoms may be very subtle. Drinking and urinating a lot, especially when urine is very dilute or clear, are the most common symptoms. Weight loss, poor appetite, throwing up, and bad breath may be noted as well. Depending on what has caused the kidneys to fail, other symptoms may be present, such as straining to urinate or diarrhea.
Bloodwork and urinalysis are commonly performed to diagnose kidney failure. With chronic kidney failure, checking blood protein levels, red blood cell percentage, and kidney values will help determine if too much protein is being lost in the urine (resulting in low blood protein), if the kidney disease has caused anemia, or if the kidneys are not effectively ridding toxic substances from the body and removing too much water. Other abnormal lab values may suggest what caused the kidney disease (e.g. toxin, infection). Urinalysis will show if the kidneys can concentrate the urine correctly, if protein is being lost in the urine, and if other problems are occurring in the urinary tract such as infection or kidney/bladder stones. Blood pressure, x-rays, and abdominal ultrasound may also be performed to assess the severity of disease, get an idea of how the kidneys look, and to check for potential causes.
International Renal Interest Society (IRIS) offers staging methods to help monitor and treat patients in acute and chronic kidney failure. Stages 1-4 are based on how well the kidneys can concentrate urine and filter toxins out of the blood. Laboratory values (e.g. SDMA, creatine) and urinalysis are used as criteria to move from one stage to the next, with stage 1 indicating mild kidney failure (i.e. minimal laboratory value changes) and 4 being severe (i.e. major changes). Substaging also helps determine severity and treatment needs. Substaging in chronic failure is determined by how much protein is in the urine and if high blood pressure is present.
Kidney failure can happen at any age, but chronic kidney failure is more common in older dogs. No breeds or gender are specifically prone to the disease.
Chronic kidney failure cannot be cured and treatments will be needed for the remainder of the pet’s life. Diet change can be very helpful. Prescription diets low in phosphorus, sodium, and protein as well as high in fiber, calories, and omega 3 fatty acids have been shown to increase the lifespan of dogs with chronic renal failure. Canned diets may be better than dry diets because they increase fluid intake, which helps combat dehydration.
Periodic subcutaneous or intravenous fluid administration may be needed, depending on how severe the chronic kidney disease is. Fluids help combat chronic dehydration and help flush the kidneys and remove bodily toxins. While scientific studies have not proven that daily or weekly fluid therapy increases lifespan, it does make pets feel better. Most dogs eat better and are more active after treatments.
Medication to decrease blood phosphorus levels may be given if phosphorus gets too high. Treatment for anemia may also be needed. This can include giving a blood transfusion or giving a medication to simulate erythropoietin. Pets with high blood pressure will need hypertension medications (e.g. benazepril, amlodipine). Some of these medications may also be helpful for decreasing protein in the urine (i.e. benazepril). Appetite stimulants and gastro-protective medications may be needed in pets with ulcers or toxic levels of uremia.
Renal Replacement Therapy Kidney dialysis and/or renal transplant, more commonly done in people, are rarely performed in animals. Dogs tend to reject transplanted kidneys. Dialysis, when performed, is most commonly done with acute kidney injuries, and only at certain, specialized veterinary institutions.
Veterinary cost varies quite a bit depending on the underlying cause, and how the pet responds. Initial identification tests for diagnosis usually range from $200-750. Long-term management of chronic kidney failure may range from $100-500 a month, depending on what medications are prescribed and how often fluid therapy is needed.
Unfortunately, little can be done to prevent kidney failure. Avoid exposing your pet to toxic substances. Take him or her in for yearly check ups. Monitor for changes in drinking and urinating habits to ensure treatment can be started as soon as your pet becomes sick. Always call your vet with questions/concerns.
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