Chronic Kidney Disease (CKD) in cats
Chances are, if a cat lives long enough, he will get kidney disease. 81% of cats over the age of 15 have chronic kidney disease (CKD).[1]
The kidneys are kind of the Swiss army knives of all the body organs. They perform a variety of life-sustaining chores, and none of us – not cats, dogs, humans, nor any other animals who have kidneys – can survive without them.
What do the kidneys do? Why do the kidneys fail? What treatments are available to cats with chronic kidney disease today? I try to answer these questions and more in this post.
Even if you are lucky enough to have a cat with healthy kidneys today, it’s still worth learning about this disease. If your cat is graced with a long life, you will likely face CKD eventually.
And while you can’t completely eliminate the risk of kidney disease in cats, there are things you can do to reduce her chances of getting this disease, or to catch CKD early. Knowledge and early treatment can improve your cat’s length and quality of life.
Read on.
What are the kidneys and what do they do?
The kidneys are two bean-shaped organs that are located near a cat’s rib cage, one on each side of the spine.
Considering how much these organs do, it’s hard to believe how tiny they are. Each cat kidney is only about an inch-and-a-quarter to an inch-and-a-half long.[2]
Kidneys filter a cat’s blood
One of the most important jobs that kidneys do is clean waste products from the blood and turn them into urine, which gets peed out of the body.
How does blood get so “dirty” that it needs cleaning?
When a cat eats, his body takes all the nutrients from the food, and turns them into energy.[3] All the stuff that is left over, which is now in the cat’s blood and bowels, is waste. If waste is allowed to build up in the blood, it can become toxic.
Blood is constantly circulating through the kidneys. Blood that needs to be cleaned, enters a kidney through the renal artery. It moves through progressively smaller blood vessels until it reaches the nephrons, which are the kidney’s tiny filters.
The waste that is filtered out by the nephrons becomes urine. Urine drains into a collection channel and exits the kidney through the ureter, which leads straight to the bladder (and eventually, the litter box). The newly filtered blood returns back to the body.
The kidneys filter all the blood in a cat’s body many times a day. We actually don’t know how many times cats’ blood passes through their kidneys, but in humans, our entire blood supply passes through our kidneys roughly 300 times a day.[4]
Kidneys also help keep a cat’s body “balanced”
A cat’s kidneys help maintain homeostasis in the body. Homeostasis just means “the status quo.” Kidneys help make sure that body systems don’t get out of whack.
For example: kidneys control the balance of water in the body, so there isn’t too much or too little. They control the acidity of the blood, so that it remains as close to neutral as possible.
Kidneys manage blood pressure by sending out hormones to control the contraction of blood vessels. They keep electrolytes – essential minerals that do everything from making sure the heart functions properly, to keeping a cat’s teeth strong – in balance.
Kidneys also stimulate a cat’s bones to make red blood cells, and activate Vitamin D so that it can be used by a cat’s body.[5]
What is chronic kidney disease (CKD)?
CKD isn’t actually a disease. It’s more of a description of what is going on in a cat’s body when the kidneys lose their ability to fully function from some other disease, injury, or aging.[6]
Lots of things can happen to a cat that ultimately impact his kidneys. Cats can be born with kidneys that didn’t form properly in the womb, impacting their ability to do their job over a cat’s lifetime.
A single event, like a poisoning or a car accident, can injure a cat’s kidneys.
An illness can damage the kidneys, too, and inhibit their ability to perform the way they are supposed to. Even certain drugs prescribed by your veterinarian to treat or diagnose an illness have the potential cause kidney harm.
Any one of these things can lead to the ongoing, progressive deterioration in the kidneys that we describe as “chronic kidney disease.”
What causes CKD in cats?
Here are some of the common things that can lead to CKD in cats:
Congenital diseases
Some cats are born with malformed kidneys. Polycystic kidney disease, an inherited disease which is common in longhaired cats, is one example of a congenital kidney disease.
Amyloidosis, in which abnormal proteins are deposited on various tissues and organs, including the kidneys, is also an inherited, congenital disease.
Bacterial infections
A bacterial infection of the kidneys, known as pyelonephritis, usually starts out as a lower urinary tract infection that works its way up to the kidneys.[7]
Certain tick-borne bacterial infections, including Lyme disease, can also cause kidney failure.[8]
Viral infections
Feline viral infections, including feline infectious peritonitis (FIP), feline immunodeficiency virus (FIV), and feline leukemia virus (FeLV) can damage the kidneys.
Parasite infections
Some parasites are capable of invading the kidneys, including Capillaria plica, also known as the kidney worm.
Toxins
Common household toxins – antifreeze, lily plants, human medications (especially antibiotics and over-the-counter painkillers like Tylenol and Advil), and mouse or rat poisons – can cause irreparable damage to the kidneys if consumed by a cat.
Other diseases
Hyperthyroidism, which causes high blood pressure in cats, can damage the kidneys.
Heart failure with low blood pressure can also cause harm to the kidneys.
Clotting disorders, certain cancers, and immune disorders can all affect kidney health.
Injury and illness
A cat who loses too much blood after being hit by car, for example, would suffer low blood pressure that could impact the kidneys.
Overheating in hot weather, or extreme vomiting and diarrhea, can all cause a rapid drop in body fluids that can affect the kidneys.
Why are cats so prone to kidney disease?
Why do so many cats seem to end up with kidney disease?
The short answer is that scientists and veterinarians don’t know (yet). But there are two factors that probably contribute:
Cats have fewer nephrons
Cat kidneys are overbuilt. Cats need only a small percentage of the nephrons they were born with to survive. But, cat kidneys still don’t have as much spare nephron capacity as human or dog kidneys.
Cats have about 200,000 nephrons in each kidney, while dogs have twice that many, and humans have a million nephrons in each kidney.[9]
In other words, other animals just have more nephron wiggle room should their kidneys become damaged.
Cats don’t drink enough water
Chronic dehydration may be a risk factor for kidney disease. The kidneys are hardworking organs and they need hydration to do their job properly. Blood valves need to be open, waste needs moisture so it can be flushed, and nutrients need to be able to flow easily to the kidneys.[10]
Cats are notoriously fussy water-drinkers. I’ve written a whole post about why cats don’t seem to drink enough, and what you can do about it.
And it might just seem like cats are particularly vulnerable to kidney disease versus other animals. It’s estimated that more than 50% of humans over the age of 75 suffer from kidney disease, too.[11] It is likely that just aging can cause the kidneys of all creatures to eventually fail.
What kinds of cats tend to get kidney disease?
Kidney disease is mostly a problem for mature and senior cats. Kidney disease affects 30-40% of cats older than 10, and 81% of cats over 15.
Only 10% of cats younger than 3 years old will have kidney disease.[12]
Are certain cat breeds more prone to kidney disease?
Certain cat breeds seem to be more prone to inheritable types of kidney disease. These cat breeds include:
What happens when a cat’s kidneys aren’t working properly?
In the early stages of disease, the kidneys deal with damage by simply producing more urine. The kidneys lose their ability to filter, so they compensate by flushing waste out with lots of water. Cats will tend to drink more water to make up for all the moisture that is being turned into pee by the kidneys.
One problem is that the baby gets thrown out with the bath water: protein and vitamins get flushed out, too, along with the waste. The loss of important nutrients can affect a cat’s appetite and impact many body systems.
Once two-thirds of the kidneys have failed, there is a rapid rise in waste in the bloodstream that the kidneys just can’t keep up with. The kidneys don’t have the ability to filter the waste, nor are they able to simply flush it all out. This is when cat guardians typically begin to notice symptoms of illness in their cats (see the symptom list below).
Failing kidneys also means that blood pressure isn’t being properly regulated. High blood pressure can impact a cat’s eyes, brain, and heart.
When kidneys are unable to do their job, acid builds up in the blood, which affects the function of a variety organ systems.
Failing kidneys may mean that a cat is unable to produce red blood cells, leading to anemia, where there aren’t enough red blood cells to carry oxygen to a cat’s body tissues.
What are the symptoms of CKD?
The early signs of CKD are often misattributed to “normal aging.” They include:
- Weight loss
- Poor coat quality[13]
As the kidneys continue to fail, additional symptoms of CKD include:
- Bad breath
- Poor appetite
- Drinking more
- Urinating more
- Vomiting
- Diarrhea
- Lethargy (tired, lacking in energy)
- Mouth sores
- Cat appears unkempt (scruffy, ungroomed)
- Fever
- Peeing accidents, or an inability to urinate
- Lower back pain
- Swelling in the limbs[14]
How is CKD diagnosed?
Diagnosing CKD can be very challenging. The “problem” (in quotes, because it is also a lifesaving gift) is that cats have enough spare capacity in their kidneys that they can lose up to two-thirds of their kidney function before it starts to affect their health. A cat’s kidneys can be quietly failing for months or years before a cat guardian or veterinarian might even notice.
Traditional tests for kidney disease: blood urea nitrogen (BUN) and creatinine, are “late markers” for kidney failure. That means that they don’t show that a cat is sick until CKD is quite far along.
Today, there is a relatively newer test that can determine if early kidney disease is occurring. A blood test for SDMA (symmetric dimethylarginine), acts like an early warning system that the kidneys aren’t filtering the blood the way they should.[15]
SDMA can detect as little as 25-40% reduction in kidney function, compared to 75% loss of kidney function for the creatinine test, for example.[16]
The main concern with this newer test is that there haven’t been any large-scale studies in cats on its use. When in a cat’s life should veterinarians begin offering this test to patients? How often should the test be repeated before kidney disease is diagnosed? What other factors affect SDMA in a cat’s blood? How should SDMA test results be analyzed?
And most importantly, we need studies to show that early intervention improves outcomes for cats with CKD.
We don’t have all the answers yet.
What other tests are used to diagnose kidney disease in cats?
All tests for kidney disease are looking for higher concentrations of waste and other substances in a cat’s blood and urine that healthy kidneys would be filtering out. A veterinarian may recommend more than one test to confirm the findings of other tests.
Ideally, cat’s blood will be tested a second time, some weeks or months after the first test (and after fasting), before a vet diagnoses a cat with CKD, as there are many ordinary things, like dehydration, that can provide inaccurate readings.
Blood urea nitrogen (BUN)
This test looks for urea nitrogen, a waste product that is created when a cat’s body breaks down the protein that she eats. A higher BUN could indicate kidney failure.
Creatinine (CREA)
Creatinine is a waste product that comes from digesting protein and from the normal use of muscles. A creatinine test measures how well the kidneys are filtering waste from the blood. Too much creatinine suggests kidney damage.
Electrolytes
It’s the kidneys’ job to keep electrolytes such as sodium, potassium, chloride, bicarbonate, phosphorous, and calcium in balance. If electrolytes are unbalanced, it could be a sign that the kidneys aren’t working properly.
Complete Blood Count (CBC)
A complete blood count is literally a count of a cat’s red and white blood cells and platelets.
The kidneys are responsible for producing a hormone called erythropoietin that stimulates the production of red blood cells. If the kidneys aren’t able to produce all the erythropoietin that a cat needs, the red-blood-cell count may be low.
If the cause of the kidney disease is an infection or inflammation, a CBC would show an increase in white blood cells.
If the underlying cause of the kidney disease is a clotting disorder (which is rare), the platelet count would be low.
Urinalysis
Urine is a window into kidney function. A Urine Specific Gravity (USpG) test will show how diluted or concentrated a cat’s urine is. A higher number means that the urine is more concentrated, and is a good sign that the kidneys are still able to conserve water.
A urine sediment test can show if there is protein, bacteria, blood cells, or kidney cells in the urine. Any one of those could be an indication of kidney infection or damage.
A urine culture is also important because cats with CKD are more likely to have urinary tract infections (UTIs).
Other tests
Your vet may also recommend X-rays or ultrasounds to look for kidney stones, cysts, or areas of dead tissue.
He or she will likely check your cat’s blood pressure. High blood pressure could be both a sign and/or a cause of kidney damage.
Rarely, a vet may recommend a kidney biopsy to find out the type of disease that your cat is suffering from.
How is urine collected from a cat for a urinalysis?
You can’t exactly ask a cat to pee in a cup, can you?
There are three ways of collecting urine from a cat:
Non-absorbent litter
Your vet may recommend using a non-absorbent cat litter in your cat’s usual box. The pee will just settle in the bottom of the litter pan, and you can tip the box so that all the urine collects in a corner. You can then suck up a sample with a syringe or eye dropper.
If that doesn’t work, your vet will be able to extract urine from your cat using:
Catheterization
Catheterization involves inserting a small tube into the cat’s urethra (the opening where the pee comes out) up into the bladder. Cats will need to be sedated for this procedure.
Catheterization can cause some irritation to the urethra, and can also introduce bacteria from the outside world into your cat’s bladder. But it’s less invasive than cystocentesis (below).
Cystocentesis
Cystocentesis involves inserting a very fine needle through your cat’s belly wall into her bladder.
While this procedure is considered safe and produces the “cleanest” urine sample, not all cats will lie still for the procedure. So, this test may also require sedation. Cystocentesis also requires a relatively full bladder, and may necessitate the use of an ultrasound to locate the pee within the bladder.
How do I know how bad my cat’s CKD really is?
There’s a system that all vets use to measure the progression of kidney disease in cats. It’s called the IRIS system, which stands for The International Renal Interest Society.
Staging kidney disease based on a system like IRIS is useful. Knowing where a cat “is” in a progressive illness like CKD, can help guide the treatment plan.
The IRIS system breaks kidney disease down into four stages:
Stage I
In this earliest disease stage, a cat has no symptoms. His BUN and creatinine tests are normal. It’s rare to diagnose a cat with CKD at this stage because there are no outward signs of illness, and no change in his lab values. But CKD, caught at Stage I, has the best chance for successful treatment.[17]
Sometimes CKD in Stage I is discovered by a vet simply palpating (feeling) the kidneys or seeing the kidneys on an X-ray or ultrasound. Sometimes a vet will notice that a cat’s blood creatinine is increasing over time, even if it’s still in the normal range. Protein that keeps showing up in urine can be another sign.[18]
Cats in Stage I and II are typically treated with a prescription cat-food diet and monitored.
Stage II
Some cats will have started to drink more and pee more at Stage II. Your vet can see changes in your cat’s blood work and urinalysis that indicate changes going on in the kidneys.
Your vet will probably want to discontinue any drug that your cat is taking that could be harmful to the kidneys (if possible). He or she will try to identify and treat any infections that could be causing loss of kidney function.
Stage III
Cats in Stage III often appear sick. There is more waste in the blood work. Cats in Stage III (and also IV, below), can be given erythropoietin injections to help with anemia. They can be given supplements to help with low potassium, and phosphorous binders to treat high phosphorous.
Drugs that reduce nausea and vomiting can help a cat with a poor appetite, or one who is vomiting frequently. Fluids can be given intravenously or under a cat’s skin, to help with dehydration. You can learn to give your cat these medications and fluids at home.
Stage IV
Stage IV is the final stage of renal failure when cats are often in crisis.
What is a prescription kidney diet?
Prescription kidney diets are designed with less protein, phosphorus, and sodium than traditional cat food to help reduce the amount of waste in the bloodstream that a cat’s kidneys will have to process.
Prescription kidney diets are often higher in water-soluable vitamins, fiber, and antioxidants to help improve a cat’s quality of life.
However, many cats are fussy about eating their therapeutic diets. Not eating, even for a very short period of time, can cause a fatal liver disease in cats called hepatic lipidosis.
Transition slowly from your cat’s favorite food to the new prescription diet. Warm the food to make it more enticing. Add vet-approved toppers, like the juice from a can of tuna, or possibly bone broth. Even though prescription cat food is expensive, you may have to try different brands to see if there is one your cat likes.
But first talk to your vet if your cat is not eating. There may be other options, like adding a phosphorous binder to his favorite food instead of using the prescription diet, if your cat is refusing to eat her special food.
Can chronic kidney disease (CKD) be cured?
No. Chronic kidney disease can only be treated, not cured. Any damage to the kidneys cannot be reversed.
That doesn’t mean there isn’t anything veterinary science can do! There are lots of tools in your vet’s toolbox that can help extend and improve your cat's quality of life:
Antibiotics
Antibiotics can be used treat infections that have caused kidney disease or are the result of kidney disease. Cats with CKD tend to develop bladder infections more frequently.
Potassium supplements
Cats with CKD tend to lose potassium in their urine, which leads to muscle weakness, stiffness, and a poor coat quality. Low potassium can also make CKD worse.
B vitamins
When the kidneys can no longer concentrate urine, water-soluble vitamins, like B12, get washed out in a cat’s pee. Supplementing with extra B vitamins can be very helpful.
Blood-pressure lowering drugs
High blood pressure can be caused by CKD, and can also cause additional damage to kidneys. Angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and calcium-channel blockers (CCBs), are medications that can help do the job the kidneys are no longer able to do.
Anti-nausea and anti-vomiting drugs, and appetite stimulants
Cats who are nauseous and vomiting often have no appetite. These medications can help a cat regain interest in his food.
Anemia medications
Many cats with CKD aren’t able to produce enough red blood cells in their bone marrow. Erythropoietin-replacement therapy can help stimulate the production of red blood cells.
Medications for proteinuria
Proteinuria is the loss of protein in the urine that is a hallmark of CKD. Proteinuria can also damage kidneys further if it isn’t treated.
Phosphate binders
Phosphate binders, usually added to food, can help “mop up” excess phosphate in the blood that is caused by CKD.
Fluids
In the later stages of CKD, cats can’t drink enough to maintain healthy hydration. Fluids can improve their quality of life.
Can a cat with CKD go on dialysis?
Dialysis, more formally known as hemodialysis, is a mechanical way of purifying the blood.
Dialysis is a treatment choice for humans experiencing acute or chronic kidney failure. A person who requires dialysis will need it for the rest of their lives, or until they are able to get a kidney transplant.
A cat undergoing dialysis would have a catheter placed in her jugular vein and her blood would be circulated through machine with a filter to remove the toxic waste that the kidneys can no longer filter. Dialysis usually takes five to six hours per session and requires two to three sessions per week, all under general anesthesia.
It can be difficult to find a center that provides dialysis for animals, and especially for cats. It is also extremely expensive.
But more importantly, dialysis can be very hard on a cat’s body, and will most certainly impact a cat’s quality of life. For these reasons, it is not usually recommended for cats who have chronic kidney disease.
Can you prevent chronic kidney disease in cats?
Most causes of chronic kidney disease are not preventable.
What you can do is limit your cat’s exposure to kidney-damaging things, like lilies, human medications, household cleaners, and antifreeze. Block access to your garage, and lock up dangerous substances.
You can keep your cat up to date on vaccines, and heartworm and flea-control medications. Doing so will help prevent many bacterial and viral causes of kidney disease.
Limit your cat’s exposure to other cats who might spread illness to your cat. The best way to do that is to keep your cat indoors.
What is the life expectancy of a cat with chronic kidney disease?
Cats are amazingly resilient. Cats with as little as 5% kidney function can survive for a surprisingly long time.[19]
Many cats, especially those diagnosed with CKD in the early stages, with lifestyle changes and long-term management of the disease, can go on to live a normal lifespan.[20]
In general, CKD tends to progress slowly, and some cats respond very well to treatment. If your cat has been diagnosed with CKD, she may still have years of active life left with treatment.
If your cat is experiencing end-stage renal disease…
It can be hard to know when the end is near for a cat in the final stage of a disease like CKD. What are the signs that a cat is near death? How do I know if my cat is suffering? What is the right thing to do?
This extensively researched website, created by a woman who had three cats with CKD, does an incredible job of answering some of these harder questions.
I found this page, entitled “The Final Hours,” especially helpful. It outlines the signs and symptoms that might accompany a cat with CKD near the end, and provides guidance as you navigate the difficult decisions that come with loving a cat.
Tanya’s Comprehensive Guide to Feline Chronic Kidney Disease
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Dawn LaFontaine is a lifelong animal lover who always seems to have a little pet hair in her keyboard. Her blog, Kitty Contemplations, helps cat guardians better understand and care for the special beings they share their lives and homes with. Her cat-products business, Cat in the Box, sells beautiful, well-made, and award-winning products that she designed to meet the biological needs of cats.
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FOOTNOTES
[1] Weir, Malcolm Weir, et al. “Chronic Kidney Disease in Cats: VCA Animal Hospitals.” Vca, vcahospitals.com/know-your-pet/kidney-failure-chronic-in-cats. Accessed 4 Oct. 2024.
[2] “Kidney Size.” Kidney Size - an Overview | ScienceDirect Topics, www.sciencedirect.com/topics/immunology-and-microbiology/kidney-size. Accessed 4 Oct. 2024.
[3] “Overview of Kidney Disorders.” University of Rochester Medical Center, www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P08231. Accessed 7 Oct. 2024.
[4] “Understanding Kidneys, Facts and Functions.” ERA, 10 Oct. 2023, www.era-online.org/publications/understanding-kidneys/.
[5] Kearley, Michael. “Kidney Disease in Cats.” PetMD, 9 May 2022, www.petmd.com/cat/conditions/urinary/kidney-disease-cats.
[6] “Chronic Kidney Disease.” Cornell University College of Veterinary Medicine, www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/chronic-kidney-disease. Accessed 3 Oct. 2024.
[7] “Pyelonephritis in Cats: VCA Animal Hospitals.” Vca, vcahospitals.com/know-your-pet/pyelonephritis-bacterial-infection-of-the-kidney-in-cats. Accessed 8 Oct. 2024.
[8] “Ticks and Your Cat.” Cornell University College of Veterinary Medicine, www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/ticks-and-your-cat. Accessed 8 Oct. 2024.
[9] Sharon M. Gwaltney-Brant, Chapter 18 - Renal toxicity, Editor(s): Ramesh C. Gupta, Veterinary Toxicology (Second Edition), Academic Press, 2012, Pages 264-277, ISBN 9780123859266,https://doi.org/10.1016/B978-0-12-385926-6.00018-1. https://www.sciencedirect.com/science/article/pii/B9780123859266000181
[10] “Not Just 4 Paws Animal Hospital: Veterinarian in Canyon Lake, CA.” Not Just 4 Paws Animal Hospital | Veterinarian in Canyon Lake, CA, notjust4pawsanimalhospital.com/dehydration-and-kidney-failure. Accessed 8 Oct. 2024.
[11] “Aging and Kidney Disease.” National Kidney Foundation, 12 Aug. 2024, www.kidney.org/aging-and-kidney-disease.
[12] Weir, Malcolm Weir, et al.
[13] ibid.
[14] Kearley, Michael. “Kidney Disease in Cats.” PetMD, 9 May 2022, www.petmd.com/cat/conditions/urinary/kidney-disease-cats.
[15] “Renal Amyloidosis.” Cornell University College of Veterinary Medicine, www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/renal-amyloidosis. Accessed 4 Oct. 2024.
[16] “SDMA in Cats: How Useful Is It and When to Use It.” Exploring SDMA Significance and Optimal Application in Feline Diagnostics, www.moichor.com/blog-post/sdma-in-cats-how-useful-is-it-and-when-to-use-it. Accessed 8 Oct. 2024.
[17] Case, Jamie, and Barri J. Morrison. “Kidney Failure in Cats: Symptoms, Stages and Causes.” PetMD, 29 July 2024, www.petmd.com/cat/conditions/urinary/kidney-failure-in-cats.
[18] “Testing for Kidney Disease: VCA Animal Hospitals.” Vca, vcahospitals.com/know-your-pet/kidney-disease-testing. Accessed 9 Oct. 2024.
[19] Case, Jamie, and Barri J. Morrison..
[20] Kearley, Michael. “Kidney Disease in Cats.”.