My vet told me my cat has kidney disease – but what does that mean? They were throwing around jargon like B-U-N and creatinine and specific gravity. What the heck is an azotemia, and is it bad? I came in because my older cat was drinking more water going to the litter box more often. I thought she just had a urinary tract infection and needed antibiotics.
This is an all too common scenario. A senior cat is seen drinking from the water bowl more and the litter box needs to be emptied more frequently. Both typical signs of a simple urinary tract infection. Except that this elderly cat doesn’t have a bladder infection or need antibiotics – they have chronic kidney disease (CKD) or chronic renal failure (CRF), which can have very similar symptoms, but also include weight loss, unkempt hair coat and appearance, lethargy, and weakness among others.
So, what is chronic kidney disease?
The kidneys are made up of thousands of filtration systems called nephrons. The nephrons are responsible for filtering wastes into the urine and maintaining our water and electrolyte balance, primarily. They also keep a couple of our hormones in check. In chronic kidney disease, the nephrons are injured or destroyed and can no longer perform these basic functions. Blood urea nitrogen (BUN) and creatinine (CREA) are waste products from the kidney that build up in the blood when the nephrons are failing or have been destroyed and are the primary values we measure on basic bloodwork to tell us if the kidneys aren’t functioning properly. An elevation in both the BUN and CREA is called azotemia. Along with measuring BUN and CREA, a urine specific gravity (USG) is monitored as a measure of urine concentration – how well the kidneys are holding onto water to keep the pet appropriately hydrated. When the nephrons are lost, more water is lost into the urine, making the urine more dilute. The more dilute the urine, the more water is lost, the more dehydrated the pet becomes even though they seem to be drinking more than enough water.
Along with losing water, the kidneys will also leak protein into the urine when the nephrons are damaged. This is what causes the slow and steady weight loss – their body is not able to maintain their muscle mass from the food they take in when it’s being lost through the kidneys. It’s sometimes difficult for owners to see the weight loss because it comes on so gradually until the cat is weighed.
The term chronic indicates that the condition has been coming on for a while – usually greater than 3 months. However, the limitations of the bloodwork are that at least 75% of the nephrons have to be nonfunctioning before the BUN and CREA will start climbing so it looks like it’s a sudden change when it’s really not. In most cases, we never know what initially caused damage to the kidneys that led them to fail. Some infections and toxins are known to injure the nephrons and we know age plays a big role, but we usually never identify the inciting cause.
Now that I know what it is, what do I do to treat it?
Unfortunately, there is no cure for chronic kidney disease, but needs to be managed as best as possible. This typically involves a diet change to a kidney friendly, low protein food and encouraging as much water as possible. Sometimes, owners will need to consider administering fluids to their cat daily to keep up with the water loss by the failing kidneys. However, not all cats are candidates for this treatment, not all cats will tolerate fluid therapy, and it can become stressful for the owner. In some cases, daily medications and hormone therapy will also be recommended.
Depending on how mild or severe the case is will sometimes provide a guide as far as prognosis is concerned. With early detection and proper management, cats can sometimes live for years with their kidneys not functioning at full capacity. This is why routine senior bloodwork is critical. However, once the cat is diagnosed, frequent monitoring is always recommended to make sure nothing changes too rapidly. Cats are notorious for being stoic animals and sometimes won’t tell their owner that something is wrong until they are very sick, possibly irreversibly so. Every cat’s case is different and there is not a “one size fits all” treatment for each patient. What we do know is that chronic kidney disease is one of the most common conditions diagnosed in older cats and needs routine monitoring and management.