Causes
There are two types of kidney failure in cats. Each has different causes, treatments, and outlooks.
Acute Kidney Disease or Acute Kidney Injury (AKI) develops suddenly, over a matter of days or weeks. It happens in cats of all ages and is usually the result of:
• Poisons, which are the most common cause of acute renal failure. Antifreeze, toxic plants like lilies, pesticides, cleaning fluids, and certain human medications are highly poisonous to your cat’s kidneys. Even a single tablet of ibuprofen can lead to their kidneys shutting down. Check around your house and garage for these substances and make sure your cat can’t get into them.
• Trauma, especially involving a broken pelvis or burst bladder.
• Shock from losing a lot of blood quickly or rapid dehydration; overheating in hot weather, a significant rise in activity, vomiting, and diarrhea can all cause a big dip in body fluids.
• Infection in the kidneys.
• Blockages that change the flow of blood into the kidney and the flow of urine out of it (such as in a male cat that can't urinate because of a urethral blockage).
• Heart failure with low blood pressure, which reduces blood flow to the kidneys.
Note: If diagnosed in time, acute kidney disease can often be reversed!
Chronic Kidney Disease (CKD) problems can be harder to treat. Found mostly in middle-aged and older cats, they develop over months and even years. If your cat is 7 years or older, pay special attention to their health.
While the exact causes of chronic kidney disease aren’t always clear, even to vets, they include:
• The most common cause of progressive kidney failure in older cats is interstitial nephritis, which is a combination of inflammation, cellular degeneration, and scar tissue formation. Interstitial nephritis may be triggered by infections or other injury to the kidneys earlier in life. In most cases, the exact cause cannot be determined.
• Kidney infections and blockages, which may not result in acute renal failure, but wear down kidney function at a low level for months or years.
• Other conditions, from advanced dental disease and high blood pressure to thyroid problems such as hyperthyroidism, and cancer.
Symptoms
• Excessive urinating - More than 4 trips to the litter box per day is a bad sign.
• Excessive thirst - Considered more than 100ml per kg of their bodyweight per day.
• Bacterial infections of the bladder and kidney - These develop more easily in the diluted urine produced by failing kidneys.
• Weight Loss.
• Loss of Appetite.
• Nausea.
• Loose Stools.
• Bloody or cloudy urine.
• Mouth ulcers, especially on the gums and tongue.
• A brownish-colored tongue.
• A dry coat.
• Constipation.
• Weakness.
• Edema (fluid-filled swelling in the limbs).
Note: When kidneys start to fail, they become less capable of removing waste from the bloodstream. As this waste builds up, your cat's breath will smell worse.
The bad breath associated with late stage kidney disease commonly has an ammonia/urine odor.
Blood Tests / CKD Stages
Blood Tests For CKD
BUN (Blood Urea Nitrogen) is one of three blood tests for kidney function. It is a good screening test but not perfect, as it only elevates significantly if kidney function has deteriorated by 60% to 70%. However, it is inexpensive to run and part of most blood panels. BUN is also affected by diet, exercise, and muscle mass, so results can be skewed due to non-kidney factors; increased results must be interpreted in light of these factors.
Creatinine refers to an amino acid constituent of muscle protein. Like BUN, this test also doesn’t show significantly elevated results until kidney function has deteriorated by 60% to 70%. It is also affected by diet, exercise, and muscle mass, though not as much as BUN is. Blood profiles that incorporate only these two tests can accurately diagnose kidney disease once the disease has progressed to a later stage, but are not so good at diagnosing very early disease.
SDMA (Symmetric Dimethylarginine) is a third test which tests for the amino acid arginine, which may be incorporated into the blood panel. SDMA levels elevate very early in the course of kidney disease, anywhere from 12 to 36 months before BUN and creatinine elevate (reflecting only 25% kidney damage versus 60% to 70%).
Other blood tests that can help diagnose cats with kidney failure include measuring blood levels of phosphorus and calcium. Phosphorus, in particular, tells us about the severity of kidney issues since it elevates when the kidneys are severely damaged. Cats with elevated blood phosphorus levels and elevated levels of the kidney enzymes just mentioned are much harder to treat and have a poorer prognosis.
Four Stages of CKD
CKD is classified into four stages, based on the severity of clinical signs and blood tests. These are often progressive, though the timeline may vary:
Stage 1: The creatinine level in the blood test is lower than 1.6, which means that less than 66% of kidney function has been lost. At this stage, I suggest that you feed your cat a wet food diet only, and one with a protein level no lower than 40% on a Dry Matter Basis. Any lower and you risk causing muscle wasting.
For a better understanding of muscle wasting in cats, please visit my Weight Loss page.
Stage 2: The creatinine level is between 1.6 and 2.8, which means that 66% – 75% of kidney function has been lost. At this stage, I recommend giving your cat Azodyl twice daily and scheduling a follow-up blood test in 6 months.
Stage 3: The creatinine level is between 2.9 and 5.0, which means that 76% – 90% of kidney function has been lost. At this stage, continue giving Azodyl. I would also suggest a subcutaneous (sub-q) fluids treatment to combat dehydration and ease the burden on your cat’s kidneys. Your vet can suggest dosing and frequency.
Stage 4: The creatinine level is higher than 5.0, which means that 90% of kidney function has been lost. At this stage, your cat may be suffering quite a bit, so it is important to keep your feline friend as comfortable as possible. Your cat may lose its appetite and at this point an appetite stimulant would be recommended. Continue feeding healthy wet food only and steer clear of the kidney prescription diets. I'd also continue giving Azodyl and recommend increasing the frequency of the sub-q fluids.
Bloodwork Summary Chart
I have prepared a "Bloodwork Summary Chart" that is available for download in two formats. This chart will help you keep track of the important blood tests during your visits to the vet.
Click here for the Excel version of the chart.
Click here for the PDF version of the chart.
I have also prepared a guide called "Common Blood Tests For Cats." This guide will help you identify the more commonly prescribed blood tests by your vet.
Click here for the PDF version of the guide.
My Cat's Progress
Here are Motor's CKD lab results for the last six months under my treatment plan:
BUN 74 - 41 (improvement)
Creatinine 6.3 - 4 (improvement)
SDMA 34 - 27 (improvement)
Treatment
If you or your vet suspects CKD, the vet will first perform blood and urine tests. X-rays, an ultrasound or biopsy might also be needed to make a diagnosis.
If kidney disease is found, treatments can include: surgery, removal of blockages, IV fluids, diet change, medications and/or supplements such as Azodyl. You may also be able to inject fluids under your cat’s skin at home. This is known as subcutaneous or sub-q fluids.
As of 2023, it's true that you can't reverse CKD in cats. However, you can slow the progression, and even lower the BUN, Creatinine and SDMA with the right treatment.
Over the years, I've used a four-pronged approach with great success. The anacronym for my approach is F.A.D.E. which stands for Fluids, Azodyl, Diet, Enulose.
Fluid Therapy
Subcutaneous (sub-q) fluids will deliver fluids to your cat so they will continue to maintain proper hydration levels on a regular basis. This helps the kidneys to better process out the toxins.
As a general rule, the average sized cat should receive 75-100ml of fluids at one time. How often cats are given fluids depends on the severity of their condition. Fluids can be administered as little as twice a week to every day if needed.
For instructions on how to give fluids at home, please download my PDF guide Subcutaneous Fluid Therapy.
If you've never done this before, please take your cat to the vet and have a tech demonstrate the process at least once. Once home, remember to give your cat a treat after fluid therapy. You can also try to feed your cat during the procedure to help them focus away from the process.
Azodyl
Azodyl is a powdered probiotic in a tiny capsule. Most vets know about Azodyl, but to my surprise, some have never heard of it. It should be noted that Azodyl, like most all probiotics, retain their potency best if kept refrigerated. And although you can get Azodyl on-line a little cheaper than at the vet's office, the on-line shipping ends up hurting the potency and effectiveness as the product isn't kept cold enough in the shipping container.
My advice is to purchase Azodyl at the vet's office and keep it cold on the way home…then put it in the fridge ASAP. Dosing is twice daily, and it's important to wait at least 2 hours after a feeding before giving Azodyl, and then after dosing, wait at least 1 hour before offering food again. This allows Azodyl to be the most effective while on an empty stomach!
If you have trouble pilling your cat with just the capsule, you can try placing the capsule in a Pill Pocket. My method of dosing my cat Motor, is by using a 10ml dosing syringe. I first empty the Azodyl capsule onto a very small sheet of paper with a fold in it. I then separate the syringe into the two halves. While keeping my finger over the tip of the syringe, I fill it with an 1/8" of wet food juice (preferred) or just water. Grab the sheet of paper, and while keeping it folded, empty the powder into the syringe. Then push the plunger into the syringe over the sink, and close the syringe as far as you can without the liquid coming out. Finally, squirt it in the side of your cat's mouth. I always hold my hand under Motor's mouth when I do this, as a little drips out sometimes, at which point I just scoop it up on my forefinger and "quickly" put it in his mouth. It's a bit of a process, but in time you'll get used to it.
Diet
There's no question that a low protein diet helps the kidneys not have to work as hard, but at what cost? Personally, I've always considered one's Quality of Life when it comes to dealing with illness. In this case, I would rather treat the CKD with Fluids and Azodyl, and provide a higher protein diet to stave off weight loss, muscle wasting and anemia.
And if a higher protein diet is detrimental to a cat with CKD, you certainly couldn't tell with my cats, Motor and Glovie. Their kidney and anemia bloodwork has improved in leaps and bounds, and their muscle wasting quickly resolved by applying my FDA approach!
Note: It is also widely suggested that you not feed a CKD cat dry food. Dry food is notorious for low quality ingredients and it helps to cause constipation. It also forces the kidneys to work a little harder when filtering out the toxins. I'd stick to a wet food diet, even at CKD stage 1.
Enulose
It's also worth noting that another lesser-known tool used in the fight to help slow the progression of CKD in cats, is the use of Enulose (Lactulose Solution). It's typically used to help cats who are constipated. But the unintended (off-label) benefit of Enulose is that it acts as an ammonia detoxicant, which helps to remove ammonia from the bloodstream. If your cat isn't constipated, I'd still administer the Enulose twice daily as a preventative measure. You just might want to adjust the dosage down (maybe half) in the event your cat's stool starts to become too soft. NOTE: Enulose requires a prescription, so if your cat isn't constipated, you might have to get creative in asking for it from your vet for its off-label use.
Omega-3 Fish Oil Supplement
Omega-3 fatty acids help reduce the production of inflammatory compounds that create oxidative stress to the tissue of the diseased kidneys, thus contributing to slowed progression of Chronic Kidney Disease in cats. This works by reducing protein 'leaking' through the kidneys, which is a common symptom called Proteinuria, which contributes to weight loss in a CKD cat. You can read more about the benefits of Omega-3 fatty acids for cats on my Omega 3 Fish Oil page.