The kidneys are organs which maintain the balance of certain chemicals in your dog’s blood while filtering out the body’s wastes as urine. The kidneys also help regulate blood pressure, help regulate the production of calcium and phosphorus metabolism, and produce a hormone that stimulates red-blood-cell production called erythropoiten. As you can see, a malfunctioning kidney can cause many problems.
Let us picture the kidneys filtering mechanism. There are tens of thousands of microscopic funnel shaped tubes called nephrons. These tiny structures are responsible for filtering and reabsorbing the fluids that balance the body. These nephrons are susceptible to damage due to many causes such as poisons, aging, infection, trauma, cancer, auto-immune diseases, and genetic predisposition. If any of these occur the entire nephron stops functioning. Fortunately, due to both the reserve capacity of the kidney and the ability of the nephrons to grow larger, the kidney can still function. If damage to nephrons occurs gradually and the surviving nephrons have enough time to hypertrophy, a kidney can continue to function with as few as 25 percent of its original nephrons.
When the number of functioning nephrons drops below 25 percent or when damage occurs too suddenly for the remaining nephrons to compensate, kidney failure occurs. There are two types of kidney failure. Acute kidney failure is a sudden loss of function that is sometimes but not always reversible. Chronic kidney failure is an irreversible loss of function that occurs gradually over months or years.
Failing kidneys can’t adequately clear the blood of certain toxins. These include urea (a nitrogen-containing byproduct of protein metabolism) and creatinine (a chemical byproduct of muscle exertion). As a result, when the kidneys fail, there is an abnormally high levels of these wastes products. Other blood components normally regulated by the kidneys – such as phosphorus, calcium, sodium, potassium, and chloride – may also rise or fall abnormally. Failing kidneys may also produce extremely dilute urine or urine that contains too much protein. Healthy kidneys produce concentrated urine that is relatively protein-free.
To determine the prognosis of kidney disease, blood and urine tests are performed frequently during treatment to evaluate how well the kidneys are responding. It’s a good sign if test results swing back toward normal within the first 48 to 72 hours of therapy.
Initial test results can be remarkably similar for both forms of kidney failure. The diagnostic challenge is to determine whether the dog has acute or chronic kidney failure. Making the distinction between chronic and acute failure is crucial because the prognosis and duration of treatment for the two types of kidney disease are different (although some treatment procedures may be similar). At our practices, we recommend yearly base line lab testing starting at age 3. This protocol allows us to help determine if we are dealing with acute or chronic disease.
Acute kidney failure (fig. acute kidney failure) occurs so suddenly surviving nephrons don’t have time to compensate. This abrupt failure can occur if the kidney is damaged by an infection, or harmful substances such as antifreeze and rat poison; or certain medications, including some antibiotics and chemotherapy drugs.
Many cases of bacterial kidney diseases can be successfully treated. Leptospira is one bacterium that can cause acute renal failure. Other bacteria can also cause kidney infections, invading the urinary tract, the bladder or prostate for example, and ascending up to the kidneys. With proper diagnosis and treatment these infections can be treated effectively with antibiotics and, in most cases, result in complete recovery.
Ingesting as little as a teaspoon of ethyleneglycol-based antifreeze, which forms crystals inside the dog’s nephrons and shuts down kidney function is usually fatal. Unfortunately, this product has a sweet taste which attracts pets to drink it. (Propylene-glycol-based antifreeze is a safer way to protect your car and your dog.) Another potentially lethal substance is rat poison. If a dog eats rat poison containing calciferol (a form of vitamin D) the calciferol pushes up the dog’s calcium level, causing mineral deposits, inflammation, and other damage within the kidneys.
Ironically, treatments for some nonkidney diseases can jeopardize the kidneys. Although most antibiotics cause no harm to the kidneys, practitioners should closely monitor patients on certain antibiotics – gentamicin, for example – because of potential damage to nephrons. Cisplatin (an anticancer drug) and amphotericin B (a drug for serious fungal infections) can also cause acute kidney damage. In general, before you decide on a course of treatment for any condition, ask your veterinarian about the benefits and risks of all available options.
More reading: http://www.petshealth.com/dr_library/caninekidney.html
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