Pets with kidney disease can live years with appropriate care
Kidneys play a vital role in the body by removing harmful wastes from the blood, helping to control blood pressure, and making hormones and enzymes. Not surprisingly, then, a host of serious health problems may arise when the kidneys aren’t functioning properly.
“Chronic kidney disease has an insidious onset that becomes progressively worse. The first signs are usually that the pet begins drinking more and urinating more. This can be easy to miss, especially in a multi-animal or multi-litter box household,” says Dr. Stanley Rubin, a veterinarian specializing in internal medicine at the University of Illinois Veterinary Teaching Hospital in Urbana. Other initial signs can include progressive loss of appetite with selective eating and acute blindness in cats.
“High blood pressure can also be present with kidney disease, and can lead to injury of the eyes, central nervous system, and other organs,” explains Dr. Rubin. “Ultimately, chronic kidney disease can shorten a pet’s life expectancy.”
Kidney Disease in Pets
Kidneys are made up of thousands of microscopic units called nephrons. Within these nephrons the work of filtering waste from the blood takes place. The waste that is filtered out leaves the body as urine. This process plays a central role in regulating blood pressure, fluid balance, and electrolytes, such as sodium, potassium, calcium, and magnesium.
Many factors can cause kidney damage. Chronic kidney disease is diagnosed when there is permanent and irreversible reduction in the number of nephrons. By this time, the cause of the damage usually cannot be found.
This condition is more common in cats than in dogs, and is more likely to occur with age. It is the third most common cause of death in dogs and the second most common cause of death in cats with chronic disease.
“If we can identify and treat an underlying cause of kidney damage, such as kidney stones or leptospirosis or another bacterial infection, there is a better chance of arresting and possibly reversing the damage and preserving the remaining kidney function,” explains Dr. Rubin.
Diagnosing Kidney Disease
Usually, disease has progressed over a long period and no distinct cause is found. The problem most often is diagnosed as the result of laboratory testing.
“At annual wellness examinations, veterinarians perform routine blood and urine tests that include measuring serum creatinine and blood urea nitrogen concentrations,” says Dr. Rubin. “Creatinine is a muscle metabolism byproduct, and urea is a byproduct of protein breakdown. Both are normally removed by the kidneys, but when there is kidney dysfunction these substances become concentrated in the blood. Increases in these concentrations often indicate kidney disease.”
Veterinarians have developed a staging system for chronic kidney disease in dogs and cats. The International Renal Interest Society (IRIS) has separated chronic kidney disease into 4 categories based on blood creatinine concentration, amount of protein in the urine, and systemic blood pressure. These are useful for determining the appropriate therapy and defining the prognosis of each patient.
Blood creatinine levels are one of the factors used to gauge progression of chronic kidney disease. A creatinine reading of 2.5 mg/dl falls at the high end of IRIS stage 2, and it is not until this stage that owners typically first observe indications of disease. Owners may notice that their pet is drinking more water, urinating more, and has a decreased appetite and weight loss. Unfortunately, by the time these signs appear, about 66 percent of the total kidney mass is already non-functional.
Recently, scientists developed a new blood test that measures a more sensitive biomarker, called symmetric dimethylarginine (SDMA). This test shows elevated readings when only 40 percent of kidney mass is lost in cats, allowing for earlier diagnosis of the disease.
“SDMA is very sensitive and specific in cats. This biomarker will show elevated levels 17 months earlier than could be seen with creatinine,” says Dr. Rubin. In dogs kidney disease causes increased levels 9.5 months earlier in SDMA than in creatinine.
Once chronic kidney disease is diagnosed, appropriate treatment should be determined based on the stage of the patient.
Managing Kidney Disease in Pets
“There is no cure for chronic kidney disease, but we can help slow the progression of disease and make these pets more comfortable with supportive care,” says Dr. Rubin. “The most important parts of therapy are diets low in protein and phosphate if indicated, rehydration with balanced fluids when required, and other drugs to manage complications such as high blood pressure.”
Other forms of treatment, such as dialysis and transplants, are not readily available for pets and can be very expensive. “Dialysis is most appropriate for acute kidney injury and is available at certain specialty centers. Kidney transplants can be life-extending for cats but have not been successful for dogs,” explains Dr. Rubin.
Veterinarians will initially need to see pets with advanced kidney disease at intervals as often as every two to four weeks to monitor their body weight and recheck their blood work to see if improvements are being made or if the condition is worsening. Once their condition has stabilized, some cats may need to be rechecked only every three months.
“Stabilized patients with advanced kidney disease can live years with appropriate management, depending on the severity of the disease,” says Dr. Rubin. Pets in stage 1 or 2 chronic kidney disease can live upwards of four years after diagnosis, with cats often living longer than dogs with this condition.
If you have questions about chronic kidney disease, consult your local veterinarian.
By Melissa Giese