Chronic Kidney Disease in Cats: Causes, Symptoms, and Treatment

Kirsten McCarthy / Cats.com

Chronic kidney disease (CKD) is one of the most common diseases diagnosed in cats. In this article, we’ll review the stages of CKD, how they are diagnosed, what to expect with each, and recommended therapies.

Other Names: CKD

Common Symptoms: In early stages, increased drinking and urinating. As disease progresses, signs include weight loss, picky/reduced appetite, and vomiting.

Requires Ongoing Medication: Yes. Long-term prescription diets are a core part of therapy. Other medications may be added as needed (i.e. for high blood pressure).

Vaccine Available: No

Treatment Options: Treatment depends on the stage of CKD that is present. Earlier stages may be managed with dietary changes alone to slow progression. More advanced stages may require medications to aid in appetite, nausea, and hydration.

Home Treatment: Increased drinking and urinating is the most common sign seen and the most common frustration for owners at home. Increasing the availability of water and the number and location of litter boxes can be very helpful. Cats with CKD often develop picky appetites. Having a variety of foods on hand with a similar nutrient profile to put into rotation can be helpful. Ideally, cats with CKD would be on a diet formulated with reduced but high quality protein and restricted phosphorus. In cats that turn their noses away from prescription diet offerings, it’s at least important to make sure they are getting calories and eating something consistently.

What Is Chronic Kidney Disease?

Chronic kidney disease, also known as CKD, is more of a syndrome that describes the loss of kidney function over time.

CKD is extremely common in cats, especially those who are older. It affects 40% of cats over 10 years of age and 80% of cats over 15 years of age.

The kidneys are very important organs in the body. The process of making urine is crucial for health to remove waste products from the body. On top of that, the kidneys also play key roles in other body processes. Here is an overview of all the amazing things that kidneys do:

• Remove certain waste products through urine
• Regulate water and electrolyte balance in the body
• Play a crucial role in blood pressure regulation
• Play a crucial role in the formation of new red blood cells
• Play a crucial role in vitamin and mineral metabolism, especially of calcium, phosphorus, and vitamin D
• Assist with maintaining protein balance in the body

Each kidney contains multiple structures called nephrons. Within each nephron is a structure called a glomerulus, where filtration of blood occurs. Additional tubular structures contribute to all of the kidney’s other functions. Damage to these structures, especially the glomeruli, is what contributes most to CKD.

Damage to these structures can be slowed down, but is always progressive to some degree and ultimately irreversible.

Chronic kidney disease and chronic renal failure are sometimes used to describe the same condition, which can be confusing. But compared to a couple decades ago, our ability to detect kidney dysfunction and provide therapy options has come a long way.

Cats in the earliest detectable stages of kidney disease can still live for years afterwards, sometimes even a normal lifespan depending on when it developed. The term kidney/renal failure is now reserved more for cats who are in the later stages of chronic kidney disease where the kidneys are unable to support the body, more significant signs of illness are present, and a cat’s prognosis becomes poor.

Causes of Chronic Kidney Disease in Cats

While termed a disease, CKD does not have one specific cause. It can be thought of more as a syndrome with multiple underlying causes. But regardless of the cause, the outcome is the same where we see a slow progressive decline in kidney function over time.

I like to think of the potential causes for CKD in three categories:

1. A single pre-existing genetic or developmental condition affecting the kidneys contributes to the disease.
2. A single insult to the kidneys leads to chronic changes. We call this acute-on- chronic kidney disease.
3. A long-term effect on them predisposes and contributes to disease.

Pre-existing genetic/developmental causes

• Renal dysplasia: while rare, kittens may be born with shrunken, deformed, and poorly functioning kidneys.
• Polycystic kidney disease: The PKD gene is found in Persian cats and crosses (Himalayan, Scottish fold, British Shorthair, and others). While this used to be more common, awareness and selective breeding has fortunately made it less so.
• Amyloidosis: this condition refers to abnormal proteins called amyloid that deposit in tissues, leading to organ damage. It is seen most in certain breeds like Abyssinians, Devon Rex, and oriental breeds (Siamese and others). While it occurs more in older cats, it can rarely occur in very young cats.
• Cancer: While very rare, a type of cancer called nephroblastoma can affect very young cats due to abnormal kidney tissue growth while developing in the womb.

Acute Onset Causes

• Acute kidney Infection (Pyelonephritis): In these cases, a cat may have signs of a fever, poor appetite, and abdominal pain associated with signs of a urinary tract infection.
• Toxin Ingestion: such as antifreeze or lily plants.
• Glomerulonephritis: This is inflammation of the main filtration structures of the kidneys. Many underlying diseases may cause or contribute to glomerulonephritis.
• Kidney or Ureteral Stone: If a stone causes a blockage of urine outflow, the associated kidney will be affected. If the other kidney is not blocked, signs may not be as obvious as with a urethral stone because a cat will still be able to urinate.

Chronic Causes

• Nutritional: evidence from the last couple of years has shown that diets that are high in phosphorus, have an unbalanced calcium to phosphorus ratio, and/or that contain synthetic sodium salt phosphates increase the risk for cats to develop chronic kidney disease.
• Glomerulonephritis: chronic glomerulonephritis may occur secondary to another chronic disease a cat has or may be the result of age-related degeneration. Degeneration of the glomeruli and resulting scar tissue leads to inflammation and a continuous cycle of kidney damage.
• Amyloidosis: Amyloidosis more often affects older cats who may develop it after 7 years of age.
• Chronic kidney Infection: while pyelonephritis can be acute and severe, many cats may have no obvious signs, leading to a delayed diagnosis and chronic damage to the kidneys.
• Hypertension: high blood pressure may occur secondary to heart disease, hyperthyroidism, due to genetic risk, or from otherwise unknown causes (idiopathic).
• Hyperthyroidism: Many cats diagnosed with hyperthyroidism will have a degree of kidney dysfunction that was not apparent previously. It’s possible it develops independently in some older cats. But the higher metabolism caused by hyperthyroidism is thought to contribute to stress on the kidneys. Hypertension seen with hyperthyroidism also affects the kidneys, depending on how long it has been present.
• Reduced water intake/Dehydration: Cats normally have a very high urine concentration. This means that they have a great ability to retain water, leaving more “solid” components in their urine, like waste products.

This ability allows cats to stay hydrated while drinking very little throughout the day. This comes from their ancestry as desert animals in ancient Egypt. A cat’s urine normally looks rich to dark yellow.
While this is physiologically normal for cats, there are some who propose that a disadvantage to this evolutionary adaptation is that the reduced water intake and highly concentrated urine may over time contribute to kidney dysfunction in older cats.

Stages and Symptoms of Chronic Kidney Disease in Cats

Kidneys are small organs compared to the rest of the body but they are one of the hardest working and most important for health. Benny Marty / Shutterstock.com

The International Renal Interest Society (IRIS) is an independent organization made of veterinary specialists that has developed stages of severity for CKD, guidelines for diagnosing each stage, and therapy recommendations.

IRIS stages of CKD depend on a couple of laboratory values:

• Creatinine: This is a waste product of muscle metabolism from the bloodstream that builds up in the urine at certain degrees of kidney disease. Elevations on bloodwork coincide with a roughly 60-75% loss of kidney function.
• Blood Urea Nitrogen (BUN): a waste product of protein break-down, BUN will always elevate alongside creatinine in cases of kidney disease. Singular elevations of BUN without creatinine elevations are often unrelated to kidney disease.
• Symmetric Dimethylarginine (SDMA): SDMA is an amino acid almost exclusively excreted by the kidneys. Elevations coincide with a roughly 40% loss of kidney function, making it an earlier detector of disease.
• Urine Specific Gravity (USG): how concentrated the urine is, as compared to distilled water. Distilled water is expressed as a value of 1.000. A cat’s urine is normally over 1.040 (read as “ten-forty”). Dogs by contrast normally have a lower USG, around 1.030.
• Protein in the urine, expressed as the urine protein to creatinine ratio (UPC): kidney dysfunction can lead to protein loss through the kidneys. A high UPC can also be an indication of pressures being too high within the glomeruli, causing damage.
• Imaging of the kidneys with X-ray and/or Ultrasound: Imaging can show abnormalities like kidney or ureteral stones and abnormal kidney size or shape. Ultrasound can also be used to look for evidence of pyelonephritis, polycystic kidney disease, cancer, and tissue changes consistent with function loss.
• Phosphate levels in the Blood Serum: The kidneys play a significant role in phosphorus metabolism in the body, but high levels of phosphorus in the diet can lead to damage. This is especially true when the kidneys are already not functioning well.
• Systemic Blood Pressure: the degree of hypertension present will affect the kidneys’ long term function and a cat’s prognosis. Cats with CKD who are hypertensive will have disease that progresses more quickly if the hypertension cannot be well controlled.

IRIS Stages and Symptoms

This section explains the lab parameters of each IRIS stage as well as the signs and symptoms that are most commonly seen with each stage.

Stage I

• Creatinine <1.6 mg/dL
• SDMA <18 ug/dL

A persistent SDMA above 14 ug/dL may indicate early CKD. But even if both SDMA and creatinine are normal, Stage I may be diagnosed in cats that have kidney abnormalities found on imaging and those who have progressive increases in the UPC value.

It is my personal opinion (which is shared) that a cat with a persistent and significant drop in urine concentration (less than 1.035) that cannot be attributed to another cause likely has early kidney dysfunction even if other lab work values are still normal.

Cats in Stage I may have no signs or symptoms of illness, including any change in water intake or urine output.

Stage II

• Creatinine 1.6-2.8
• SDMA 18-25
• Urine Concentration <1.035

Cats with very slight elevations just above the reference interval (like 1.6-1.7 for example) are considered to be in early Stage II. Many reference labs may not flag a creatinine elevation until it rises above 2.0 or a little higher, highlighting the importance of using IRIS guidelines. Once the creatinine surpasses 2.0, they are considered to be in a later stage II.

Substaging by checking a UPC and blood pressure is common in later stage II.

Cats in Stage II often have increased drinking behavior and an increased urine output. Appetite is typically normal and visible signs of weight loss at this stage are uncommon.

Anemia (low red blood cell concentration) may start to be seen on blood work but often has no noticeable effect on health.

Stage III

• Creatinine 2.9-5.0
• SDMA 26-38

Urine concentration is always dilute at this point, often at what we call isosthenuric or hyposthenuric, comparing the urine concentration to that of blood plasma. Isosthenuric is similar to blood plasma at 1.008 – 1.012. Hyposthenuric is lower than blood plasma at < 1.008.

Substaging at this stage with UPC and blood pressure is extremely important, as interventions to slow down disease are still possible.

Stage III can have the most dynamic range of symptoms. Cats always have increased thirst and urination habits. The closer the creatinine gets to the 4.0-5.0 range, the more we will see cats having trouble with their appetite and consistent eating. This is the stage where cats start to get very picky with their food.

The reason is that the build up of the waste products in the bloodstream causes nausea. While mild at first, a cat experiencing mild or intermittent nausea may associate a particular food with those feelings and reject it. A new food is welcome until the same thing happens. This leads to infamous stories of owners of cats with CKD having to constantly find new foods for them to try.

Intermittent vomiting may also be seen the closer the creatinine gets to 5.0.

Weight loss, while still slower and progressive, will be noticeable at this stage. Early weight loss may not be obvious because a cat will lose muscle mass first, before fat. Cats with weight loss from disease will start to lose muscle along their spine, hips, and head but may still have plenty of “bulk” or belly fat.

Anemia on blood work is usually more noticeable. Cats can often tolerate slow, progressive anemias from CKD and this may not be treated until the red cell concentration, or hematocrit (HCT) drops below 20%.

Stage IV

• Creatinine >5.0
• SDMA >38

Substaging with UPC and blood pressure is similar to other stages and considered even more important in later stages.

With a creatinine above 5.0, cats often show very obvious signs of worsening illness. Cats may have very poor control of their urination habits, are constantly near a water bowl to drink water, and have lost noticeable weight. The loss of muscle may lead to significant weakness and unsteadiness when walking or jumping.

Appetite can be very hit or miss, with some cats unwilling to consistently eat a balanced diet. These cats may only lick the gravy from their food or eat some high value treats.

Vomiting becomes common in Stage IV, due to the elevation of waste products in the bloodstream.

Anemia may be more of a factor at this stage where a low red cell concentration may contribute on its own to weakness and a feeling of illness.

Complications of Having Chronic Kidney Disease

Hypertension (high blood pressure) is one complication of CKD in cats. Checking blood pressure is an important part of CKD staging and therapy. KOTOIMAGES / Shutterstock.com

The eventual complication of CKD in any cat is that it will progress to complete kidney failure eventually. This time period is different for every cat, and depends on how early CKD was diagnosed and the success of early therapy.

There are some other less common complications from CKD that can occur.

• Hypertensive Emergencies: high blood pressure may not be apparent in a cat with CKD, especially if it has not been checked periodically. Feline aortic thromboembolism (FATE or saddlethrombus) can occur when a blood clot lodges in a major blood vessel, causing severe pain and loss of limb function. Blood vessels in the eye may rupture, leading to the appearance of blood in the eye and blindness. Severely hypertensive cats may also just appear lethargic and reluctant to move or eat.

• Nephrotic Syndrome: this complication occurs when protein loss through the kidneys is severe. The loss of albumin, a major protein that keeps tissue fluid in balance, through the kidneys causes excessive fluid build up. This occurs most often in the abdomen but can occur in the chest, around the heart, and within tissues.

• Severe Anemia: severe anemia is uncommon with CKD but is possible. The body has the ability to adapt to slow, progressive anemia, even to levels dropping below 20%. But eventually as it continues to drop, a cat will appear very pale and weak. Loss of appetite is common as is heavy breathing from the lack of oxygen to tissues.

Diagnosis of Chronic Kidney Disease

Urine specific gravity and urine protein to creatinine ratio are both important components of assessing cats with chronic kidney disease. Yaya Photos / Shutterstock.com

Diagnosis of CKD requires the combination of parameters as outlined in the IRIS guidelines. At a minimum this requires a blood and urine sample.

• Bloodwork will provide the values creatinine, BUN, SDMA, and electrolyte values like phosphorus and sodium.
• Urine Samples are used to check the urine concentration, evaluate for urine protein loss, and check for underlying infection.
• Ultrasound is very useful to evaluate the appearance of the kidneys and gain an overall appreciation for what the organs and other tissues in the abdomen look like. Kidney size, shape, and texture can be seen. Abnormalities like cysts, tumors, and stones can be seen. The urinary collection area of the kidney, called the renal pelvis, may be enlarged in cats with a kidney infection and is reliably viewed with ultrasound.
• X-ray is used less often to work up cases of CKD but is helpful for comparing kidney size and shape as well as the presence of stones.

Treatments for Chronic Kidney Disease

Giving subcutaneous fluids under the skin at home is one common approach to treating cats in later stages of CKD. Benny Marty / Shutterstock.com

Treatments for CKD depend on the IRIS Stage the kitty is in. Interventions are more modest at first and become more intensive as the disease advances or if other issues (like protein loss or high blood pressure) are found.

Cats should always be evaluated comprehensively for any concurrent conditions that may be affecting kidney function, such as a urinary tract infection. Some veterinarians diagnosing a cat with later stage CKD for the first time may even start antibiotics as a precaution.

Stage I

A therapeutic prescription diet intended for early kidney disease is commonly recommended. Examples include Hill’s k/d Early Support and Royal Canin Renal Support Early Consult. Early stage diets are not restricted in protein, but are restricted in phosphorus and sodium.

A cat with a specific underlying abnormality leading to a Stage I diagnosis (like polycystic kidney disease for example) may have additional therapies recommended.

Stage II

A prescription diet is routinely recommended. An early stage prescription diet is still typically appropriate.

Stage III

Cats in Stage III should be started on a prescription diet that is restricted in protein levels, but is of higher quality and more digestible. There are many commercial diets available for cats with kidney disease. See our reviews of the best ones. Dietary phosphorus restriction is very important, whether through a prescription diet, or starting a phosphate binder, like Epakitin.

Appetite can be greatly affected at this stage, leading to the need for appetite stimulants. The most common appetite stimulants include mirtazapine (Mirataz) and capromorelin (Elura).

If vomiting is present, prescribing Cerenia is common to reduce vomiting frequency.

This is also the stage where discussion of giving subcutaneous fluid at home may come up. This is similar (in a way) to dialysis but much less intensive. Giving fluids under the skin at home can help a cat with CKD be better hydrated, replenish lost electrolytes, and flush pent-up waste products out of the blood stream.

Stage IV

All therapies described at Stage III apply to Stage IV. The difference is that the degree of intensity will be higher.

For example, an appetite stimulant may have been needed a couple times a week at Stage III but is now required everyday. Subcutaneous fluids may have been given once a day and now are required twice a day to achieve the same benefit.

Appetite is usually quite poor at Stage IV and a cat’s quality of life is often diminished to where end of life discussions are appropriate to have. This stage is usually where we have discussions of true “kidney failure”.

Intravenous fluids can be more effective at providing benefits by flushing the renal waste products out of the blood stream. A full day or two if IV fluids can make a cat feel better, but the effects are always temporary. The higher rate of fluids needed in these cases can also lead to a cat getting more fluids than their body can handle, leading to signs of fluid overload.

Protein loss

Excessive urine protein loss can occur at any stage of CKD. While nephrotic syndrome is the worst case scenario, there are earlier stage risks. Antithrombin III, an important protein for blood clotting, is often lost with urinary protein loss, making a cat at risk for forming blood clots. Clopidogrel (Plavix) is commonly prescribed in these cases to reduce the risk for FATE and other blood clot related disorders.

Systemic hypertension may be seen with or without urine protein loss. In either case, a medication to reduce protein loss through lowering blood pressure is also commonly prescribed.

Ace inhibitors (ACEi) like enalapril and benazepril are common. In recent years, angiotensin receptor blockers (ARBs) like telmisartan have been favored.

A catch of either medication type is that they slow glomerular filtration rate and thus can make the waste product build-up in the bloodstream worse. Both may have this effect, though ARBs are thought to provide more benefit for the risk. In cats with BUN and creatinine elevations (azotemia) on their bloodwork, lower doses of these medications are started as a precaution and are gradually increased based on lab work rechecks.

Hypertension

Like urinary protein loss, hypertension can occur at any stage of CKD. Ace inhibitors and ARBs can both be used for systemic hypertension, as discussed above. Amlodipine is also a choice for systemic hypertension in cats but it does not help with protein loss in those affected cats.

In cats that have both hypertension and protein loss, it is common to pair amlodipine with either an ACEi or ARB if necessary.

Cat Care Tips

Here are some tips to help you at home with your cat if they have CKD.

• Increased drinking and urinating is the most common sign seen and the most common frustration for owners at home. Increasing the availability of water and the number and location of litter boxes can be very helpful.
• Cats with CKD often develop picky appetites. Having a variety of foods on hand with a similar nutrient profile to put into rotation can be helpful.
• Ideally, cats with CKD would be on a diet formulated with reduced but high quality protein and restricted phosphorus. In cats that turn their noses away from prescription diet offerings, it’s at least important to make sure they are getting calories and eating something consistently.
• Subcutaneous fluids at home are not considered a “beyond reasonable” step in cats who can tolerate the process well and in owners who are comfortable handling needles and willing to learn. Your vet practice may be able to set up a demo with a veterinary nurse or assistant to help you.

Prevention of Kidney Disease in Cats

Because the true underlying cause of chronic kidney disease in a cat is rarely known, it’s hard to guarantee that any specific prevention strategy will work. However, we do know some of the ways to at least reduce risk. Early detection and intervention can also be just as important:

• Feed a diet with phosphorus levels not exceeding 3.6g/1000kcal ME (This is not always easy to determine, but see our article on phosphorus in cat foods to learn more.)
• Provide lots of access to fresh water. Cats are active water seekers and are attracted to moving/running water (like a fountain).
• Feed wet/moist foods for more daily water intake.
• Have lab work done annually with your vet, including a urine sample. In cats over 7-10 years of age, consider biannual lab work and an annual blood pressure check.
• Annual and biannual (for cats over 7-10 years) exams are important for early disease detection, even if it’s picking up on early weight loss or discussing mild habit changes seen at home.
• Keep household chemicals out of reach, especially antifreeze.
• If your cat is partial to chewing/eating plants and flowers (like mine), avoid bringing a lily into the home at any cost.
• Maintain good dental health. We know periodontal disease can lead to organs like the heart and kidneys getting “showered” with bacteria through the bloodstream. If brushing is not practical, dental treats are a runner-up. See the full list of Veterinary Oral Health Council-approved products. Annual exams are important to evaluate the need for an anesthetic dental cleaning procedure.