by Dr. Jennifer Coates
Renal (kidney) disease can be divided into two broad categories: acute and chronic. Acute renal disease develops over the course of days and usually has a single cause, such as antifreeze poisoning or a kidney infection. Chronic renal disease comes on much more slowly, and is typically diagnosed in older cats. It is the result of the gradual loss of kidney function. Most often, a cause is never identified.
The kidneys can’t regenerate themselves. When functional renal tissue is damaged beyond repair it is gone forever. The signs of renal disease start to become evident once two-thirds to three-quarters of kidney function has been lost.
The kidneys play a vital role in keeping water where it is needed—inside the body. Producing large amounts of dilute urine is one of the first signs of renal disease in cats. This can result in more frequent urination, larger and/or more numerous clumps in the litterbox, and urinary accidents around the house.
On the other hand, cats with severe acute renal disease often produce less urine than normal and as the condition progresses, may ultimately produce none at all. Their kidneys have completely shut down.
When water is being lost from the body in the form of large amounts of dilute urine, cats with renal disease become dehydrated and thirsty. At the beginning, they can compensate by drinking more water, but eventually they can’t drink enough to replace what is being lost. Sometimes cats will sit by their water bowl as if they want to drink, but just can’t bring themselves to do so.
Dehydration makes cats feel bad. They lose energy and may simply want to rest rather than take part in the activities that they used to love.
Healthy kidneys are also responsible for filtering waste products out of the bloodstream and putting them into urine to be eliminated from the body. Renal disease compromises this important kidney function, which results in increased blood levels of metabolic waste products like blood urea nitrogen and creatinine. This also makes cats feel sick.
Finally, in cases of chronic renal disease, the kidneys no longer produce enough of the hormone (erythropoietin) that stimulates the bone marrow to produce red blood cells. The result is anemia and worsening lethargy.
All of the metabolic changes that produce lethargy in cats with renal disease can also make them feel bad enough that they lose their appetite. Cats with chronic renal disease often have had a poor appetite for such a long time that they lose significant amounts of weight.
Cats with renal disease are also at higher than average risk for developing gastrointestinal irritation and ulcers. These conditions cause nausea and abdominal pain (especially after a meal), making affected cats even less likely to eat.
Cats with advancing renal disease will often start to vomit as a result of the irritation and/or develop ulcers within their gastrointestinal tract, along with other metabolic changes. Some cats also develop diarrhea, but if dehydration becomes severe enough, constipation may result.
The kidneys are vital to normal body function. When a cat has advanced renal failure, the following symptoms may become evident:
As is the case with most serious feline diseases, the sooner cats receive appropriate treatment for renal disease the better their prognosis. Some cases of acute renal disease can be cured, and these lucky cats will go on to live happy, healthy, and, hopefully, long lives. Chronic renal disease is not curable, but some cases can be managed in such a way that cats enjoy an excellent quality of life for an extended period of time.