Tuesday, March 4, 2008

Kidney Disease in Cats

The kidneys are organs which maintain the balance of certain chemicals in your cat's blood, while filtering out the body's waste as urine. The kidneys also help regulate blood pressure, help regulate calcium and phosphorus metabolism, and produce a hormone that stimulates red blood-cell production called erythropoietin. As you can imagine, 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. A complete blood count looks at the numbers of red and white blood cells and a blood chemistry panel will examine the levels of waste products and electrolytes, indications of whether the kidneys are functioning properly. It's a good sign if test results swing back toward normal within the first 48 to 72 hours of therapy.

The blood tests will determine if your cat is suffering from anemia (a lower than normal number of red blood cells, RBC). This is significant because it often indicates a drop in erythropoietin, a hormone secreted by the kidneys that stimulates RBC production. The blood chemistries will determine levels of blood urea nitrogen (BUN) and creatinine, both are indicators of the amounts of waste products in the blood. Elevations of these levels result from kidney failure.

Urinalysis measures a number of factors, including how well the kidneys are concentrating the urine. In kidney failure, urine becomes dilute. Urine may also be checked for the presence of bacteria, protein, and blood. If the kidneys are normal urine should be concentrated and there should be no blood or protein in the urine.

X-rays, ultrasound and possible kidney biopsies are also very useful in assessing kidney disease.

Acute renal Failure:

The causes of acute renal failure are many. Toxins, antifreeze, cancer, intestinal disease and dehydration are just a few. Management of acute renal failure requires hospitalization, intravenous fluid therapy, and medications to help offset the affects of toxemia associated with renal failure. Intensive therapy is essential to attempt to reverse the process.

One hopes to see positive changes within 48-72 hours of treatment. The prognosis worsens if there is no reduction in the abnormal kidney values.

Chronic renal failure (CRF):

Chronic renal failure is the result of one of several different diseases, including chronic interstitial nephritis, glomerulonephritis, and amyloidosis. Some of these are autoimmune diseases; the body's immune system actually turns on itself and attacks organs and tissues. In addition, pyelonephritis, a bacterial infection that usually starts in the bladder, is often a complicating factor that precipitates CRF.

Other causes such as polycystic kidney disease (PKD) can affect younger cats, especially Himalayans and Persians, and also lead to CRF. Cysts develop in the kidneys and grow, destroying normal tissue.

Renal amyloidosis, is another form of hereditary kidney disease that affect Abyssinian and Somali cats, and may also lead to CRF.

There is no way to prevent or stop chronic renal failure. Cats can only live with one healthy kidney, but because CRF affects both kidneys, over time it is fatal.

Severely affected cats may need hospitalization. They are first rehydrated. This is best done via intravenous fluids, and therefore must be done in a hospital or veterinary clinic. Some clinicians will allow cat owners to give subcutaneous fluids at home, though this is also frowned upon by others. It involves purchasing bags of sterile fluids and injecting the prescribed amount of fluid beneath the cat's skin on a regular basis.

Dietary management is also potentially helpful. A low protein diet is generally recommended. By decreasing the protein intake, waste products of protein digestion in the blood stream decrease. This reduces the work load of the kidneys. Some cats will eat this diet while others will refuse it.

These diets are also low in phosphorus, which is usually retained in the blood stream in cats with CRF. Chronic retention of phosphorus can lead to a mineral imbalance, resulting in calcium being leached out of the bones. Increases in phosphorus also cause severe irritation of the stomach, causing nausea. Decreasing the phosphate in the diet helps to prevent these problems.

Other therapies include:

Administration of antacids such as Alternagel, this acts as a phosphorus binding agent. This will also help control phosphorus levels. This product is available at most pharmacies, located where the antacids are kept.

Calcitriol at a dose of 2.5ug/kg/day is also sometimes recommended to help control phosphorous toxicity. This drug should not be administered if phosphorus levels are over 6.

If urine cultures are positive or on ultrasound there is indication of disease in the kidney pelvis, antibiotics should be administered for 4-6 weeks.

H2 blockers such as pepsid at a dose of 5mg every day, help with the nausea of kidney disease.
If hypertension (high blood pressure) develops amylodipine (Norvasc) is given at a dose of 0.625mg per day.

Epogen or Procrit is an injectable which may help replenish the loss of erythropoiten and help control the anemia. The use of these products is somewhat controversial.

Appetite stimulants-by prescription

Potassium supplements

Kidney Transplant-this procedure is available at about 10 clinics nationwide. Cornell University and the University of Pennsylvania in the East offer this procedure. Please consult with your veterinarian for a facility near you. As of this writing the cost is $4,000-$5,000. Kidney transplant recipients need to take medication daily to avoid organ rejection, and there are ethical considerations regarding the donor cat as well.

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