By Dr. Jean Hofve, Veterinarian Advisor
Kidney disease is a frequent problem in older cats and dogs. Kidney failure can develop in young animals, but it is far more common in pets over age 10. It is the leading cause of death in older cats.
In the Pet Food Recall of 2007, melamine contamination of pet food caused tens of thousands of cats and dogs to develop Acute Renal Failure (ARF). Many of the pets who got sick but recovered likely suffered some kidney impairment, and may ultimately develop Chronic Renal Failure (CRF). In that case, age makes no difference; animals of all ages were affected.
The kidney filter out and excrete toxins from the body through the urine. Healthy kidneys conserve water and concentrate toxins into a smaller amount of liquid to be urinated away. The kidneys have a very large reserve capacity, and symptoms of failure are not seen until approximately 75% of kidney tissue is nonfunctional. When the kidneys are damaged, they become less able to concentrate the urine. Because they’re losing water in the urine, they need to drink more—but because they’re drinking more, they urinate more. So the first and most noticeable symptom is usually an increase in water consumption and urination ("drink-a-lot, pee-a-lot syndrome").
As the kidneys lose function, other signs of CRF may occur, such as weight loss, nausea, constipation, low energy, fatigue, and poor appetite. A blood test and urinalysis should be done if you notice these symptoms, as there are many conditions that can cause them. A blood test and urinalysis are necessary to accurately diagnose CRF.
The measurement of urine concentration is called Urine Specific Gravity (USG). If the USG is low (less than 1.035 in cats, and 1.030 in dogs) and there are abnormal levels of two other compounds, then kidney function is reduced. The first, BUN (blood urea nitrogen), may be high if the animal is dehydrated, or eats a very high protein diet. However, as long as the kidneys are able to concentrate the urine, small elevations in BUN are usually not a cause for alarm. The second is a protein called creatinine.
Creatinine is a more sensitive measurement of kidney function; an increase in creatinine usually means that the kidneys are having problems. In advanced disease, an increase in phosphorus is also seen, and indicates that 85% of kidney tissue is damaged.
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