For many of us who have cats, feline kidney problems are likely something that will occur, and most likely with old cats. The kidneys are responsible not only for filtering out toxins from the blood, but are also responsible for balancing water levels, regulating electrolytes, producing hormones and keeping the body at a neutral acid level.
One of my most beloved cats had renal (“doctor speak” for kidney) disease. Goocha was a beautiful silver-chinchilla Persian who had chronic kidney failure in his final years. It caused him to lose a lot of weight, stop eating and drink water like crazy. He had a thick coat and was very loving. Watching him lose weight and not want to eat was very difficult.
Say What? Learning Kidney Disease Lingo
It’s important for cat owners to understand the terms used when discussing kidney problems.
Renal Insufficiency: This term is sometimes used instead of renal failure. Insufficiency means the kidneys are no longer performing their job as well as they could. Mainly, the kidneys’ ability to filter the blood at a proper rate is diminished. Cats, dogs and people can live for years with renal insufficiency. For example, a cat (or person) can donate a kidney, losing 50 percent of their total kidney function, and not have kidney failure.
Renal Failure: This term is used when the kidneys have lost 75 percent or more of their function, causing excessive water loss (inability to concentrate urine by reabsorbing water), salt imbalance, and altered blood pH.
Nephron: This term refers to functional “units” of the kidney. These structures are comprised of blood vessels and cells that form microscopic tubes. The blood vessels filter blood into the tubes. The tubes reabsorb sugar, bicarbonate and salts — things that your body needs. If you are dehydrated, the tubes reabsorb water, creating a concentrated urine.
Causes Of Kidney Disease In Cats
Kidney disease occurs in cats for many reasons.
Some cats are born with abnormal kidneys, termed renal dysplasia, and problems appear early on in life. Kidney cysts, termed polycystic kidney disease, are another inherited problem affecting mainly purebred cats, especially Persians. While the cysts are present at birth, many cats do not develop kidney failure until years later. Infections, cancer, diabetes, high blood pressure and heart disease can also cause a cat’s kidneys to not function properly.
So, as you can see, there are many, many causes of kidney disease. I would like to focus on the most common cause of kidney disease in cats, which is termed chronic renal failure (CRF).
Chronic Renal Failure In Senior Cats And Purebreds
Chronic renal failure is a progressive disease in which more and more kidney function is lost over time. Anything that damages the nephrons and replaces them with scar tissue can cause CRF. For most cats with CRF, the cause is unknown and the term “interstitial nephritis” is used to describe the damage to the tubules. Diet, vaccinations and genetics have all been possible causes, but no one, single issue has been found to cause CRF.
Because CRF is a progressive disease, worsening over time, it’s not surprising that as cats age, the more likely it is they will be diagnosed with CRF. One 10-year study noted that more than 60 percent of cats 10 years or older had chronic kidney disease.
While any breed of cat can develop CRF, certain purebreds (Maine Coon, Abyssinian, Siamese, Persian, Russian Blue and Burmese) are more commonly affected. Male and female cats get CRF at the same rate, but males are a bit younger when diagnosed.
Symptoms Of Chronic Renal Failure In Cats
Similar to the experiences of my own cat, “Goocha,” signs of decreased appetite, excessive thirst, weight loss, poor hair coat and lethargy are common in cats with chronic renal failure. High blood pressure develops from the damaged kidneys, which is a leading cause of retinal detachment and subsequent blindness in cats. As the disease worsens and toxins build up, ulcers can form in the mouth and on the tongue. Nausea from the toxins and stomach ulcers can lead to vomiting. The toxins can also affect the brain, causing seizures, tremors and imbalance.
Diagnosis Of Chronic Renal Failure In Cats
Traditionally, blood tests measuring levels of BUN (blood urea nitrogen) and creatinine are used to make the diagnosis. BUN and creatinine are wastes that are filtered out of the blood by the nephrons. In conjunction with analyzing a urine sample, these tests confirm that there has been at least 75 percent of functional kidney loss. CRF is staged using a protocol developed by the International Renal Interest Society (IRIS).
Blood pressure and protein levels in the urine are used along with the blood tests to place an affected cat in a category of disease, i.e., IRIS stage. The worse the BUN, creatinine and blood pressure, the greater the stage level. Cats with CRF are staged at levels I through IV. A sub-stage is given based on the presence of high blood pressure and protein loss in the urine. Staging provides guidelines for follow-up and treatment.
Because one of the biggest hurdles for veterinarians and owners is a timely diagnosis, a new test that is touted to be an early marker of kidney disease has just become commercially available by veterinary testing labs. It’s called SDMA (symmetric dimethylarginine). Researchers have found that this test can detect 30 to 40 percent loss of function versus 75 percent loss by traditional tests. SDMA levels are also not as greatly affected by weight loss. SDMA is not yet part of IRIS staging. It is also too early to know if recommendations like diet change should be undertaken if the SDMA level is abnormal, but the BUN and creatinine are OK.
Treatment Of Kidney Disease In Cats
There are four key goals of managing chronic renal failure in cats. Your family veterinarian will discuss management, rechecks and tests needed to monitor your cat.
1. Treat for the treatable and decrease risks. For example, bacterial infections can be treated with antibiotics. Certain drugs like NSAIDs should be discontinued.
2. Keep your cat hydrated. CRF cats should always have access to fresh water. They should be encouraged to drink by using running water fountains, flavored water and high water content food (canned food).
3. Manage protein loss and high blood pressure. As part of disease staging, loss of protein in the urine and development of high blood pressure is common and will worsen the disease. Medications called ACE inhibitors help manage urine protein loss. The same medication can also decrease blood pressure, but calcium-channel blockers are also used for high blood pressure.
4. Adjust diet as needed. Diets that limit phosphorus, have properly balanced electrolytes and most importantly, have limited yet highly digestible protein, should be fed to cats with CRF. A balanced, kidney-friendly diet is key to proper management of CRF.
As CRF progresses, additional medications may be needed, such as hormone therapy to help control calcium and phosphorus levels in the blood, appetite stimulants, antacids and fluid replacement.
The Outlook For Cats With Kidney Disease
Knowing the degree of CRF, or staging using IRIS, is also important in providing prognosis. For example, cats in Stage 2 live an average of three years, whereas cats in Stage 4 live an average of one to two months. As the disease worsens and complications arise, a cat’s quality of life worsens, prompting most owners to consider euthanasia versus allowing their cat to die “naturally.”