Kidney Disease in Cats

by | Jul 8, 2024

Liza Cahn, DVM

You know your cat better than anyone. You’ve memorized the way they curl into a perfect ball for a nap, the specific chirp they make when they hear the treat bag come out, and even how their tail twitches when slightly annoyed. But perhaps your feline friend is drinking a little more water than usual, or their once-lustrous coat seems a bit dull. These subtle changes could be a sign of kidney disease, one of the most common medical conditions in cats, especially as they age. 

What is Kidney Disease in Cats? 

The anatomy of the feline urinary tract. (Source: Cornell Feline Health Center)

Like us, cats have two kidneys – distinctive bean-shaped organs located within the abdominal cavity on either side of the spine. Within each kidney, there are millions of microscopic units called nephrons. These nephrons work tirelessly to remove waste products and excess substances from the blood, creating urine in the process. The urine then travels through the ureters to the bladder for storage and eventual elimination via the urethra.

The kidneys are vital organs in cats. In addition to producing urine, they are critical for several other bodily functions, including: filtering waste products, regulating fluid balance, hydration, and blood pressure, promoting red blood cell production, and maintaining pH and electrolyte balance. 

While cats are born with an abundance of nephrons, they can become damaged and non-functional over time or due to disease. If approximately ⅔ of the nephrons are damaged, a cat will begin to show signs of kidney disease, also known as renal disease. 

Types of Kidney Disease in Cats

There are two main types of cat kidney disease:

  • Chronic kidney disease (CKD): A slow, progressive loss of kidney function, over months to years. This is especially common in senior cats, affecting 30-40% of those over 10 and 81% of those over 15 years of age.  
  • Acute kidney injury (AKI): A sudden, severe (yet possibly reversible) decline in kidney function, that is often triggered by an incident such as toxin ingestion, infection, or urinary obstruction. 

While both types of kidney can be serious, early diagnosis and appropriate management can significantly improve your cat’s quality of life and may even slow the progression of disease.

Causes of Kidney Disease 

Chronic Kidney Disease (CKD) in Cats

CKD is often due to age-related degeneration, which is why it is so common in senior cats. However, in many cases, the exact cause remains unknown (idiopathic). Potential contributing factors include:

  • Congenital or breed-related conditions: Certain breeds, like Persians and Maine Coons, are predisposed to polycystic kidney disease. Other congenital conditions include renal dysplasia and amyloidosis. 
  • Infections: Untreated bacterial infections of the kidneys (pyelonephritis) can lead to long-term damage. Some systemic viral or bacterial infections can also affect a cat’s kidney function, including feline infectious peritonitis, feline leukemia virus, feline immunodeficiency virus, and tick-borne disease. 
  • Cancer: Some types of cancer can affect the kidneys, such as lymphoma.
  • Glomerulonephritis (inflammation of the filtering units)  
  • Kidney or ureteral stones
  • Secondary to acute kidney injury 

Acute Kidney Injury (AKI) in Cats

AKI is characterized by a rapid and severe decline in kidney function, associated with a specific trigger such as: 

  • Toxin ingestion: Consumption of poisons such as lilies, antifreeze, rodenticide, or certain medications. 
  • Infections: Such as pyelonephritis (kidney infection)
  • Obstructions: Blockages in the urinary tract (urethral obstructions) preventing a cat from urinating. 
  • Other systemic disease: Organ failure, shock, trauma, or low blood pressure

Symptoms of Kidney Disease in Cats

Early signs of kidney disease can be subtle, especially in cats, who are masters at hiding illness. 

Early signs of disease may include: 

  • Increased thirst (polydipsia)
  • Increased urination (polyuria)
  • Decreased appetite or picky eating

Why do cats with kidney disease drink and urinate more? As the kidneys are no longer working efficiently to filter out toxins and conserve fluid, this leads to the production of large amounts of dilute urine. Cats will then drink more water to try to compensate for this fluid loss. They may also drink more water in an attempt to help flush out toxins that the kidneys are no longer removing effectively. 

As kidney disease progresses, waste products build up in the bloodstream, making the cat feel ill. Pet parents may notice the following symptoms:

  • Weight loss
  • Vomiting or diarrhea
  • Lethargy
  • Dehydration (sunken eyes, dry/tacky gums, and prolonged skin tent) 
  • Unkempt fur coat
  • Halitosis (bad breath)
  • Painful mouth ulcers
  • Anemia (low red blood cells leading to weakness and pale or white gums)
  • Hematuria (bloody urine)

Chronic kidney disease tends to have a gradual onset. The kidneys may feel small and irregular on abdominal palpation by your vet. Acute kidney injury can cause a sudden onset of severe clinical signs and may result in anuria (lack of urine production) and enlarged, painful kidneys. If your cat is straining or unable to urinate, this could indicate a urinary obstruction which requires emergency veterinary care. 

Diagnosis of Kidney Disease

If you notice any of the symptoms above, schedule an appointment with your veterinarian promptly. They will begin by getting a medical history and performing a nose-to-tail physical exam. After this, your vet will rely on several diagnostic tests to determine if your cat has kidney disease and why. 

Bloodwork

  • Creatinine and BUN (Blood Urea Nitrogen): These waste products build up in the blood when the kidneys aren’t filtering them out properly, and their elevation is a key sign of kidney dysfunction. They also contribute to your pet feeling unwell. 
  • Electrolytes: Imbalances in potassium, phosphorus, and calcium are often seen in cats with kidney disease.
  • Red and white blood cell counts: Anemia (low red blood cells) is common in cats with CKD. Elevated white blood cells can point to infection or inflammation as a potential underlying cause. 
  • SDMA: This newer test is more sensitive than traditional bloodwork values, allowing for earlier detection and more accurate diagnosis of kidney disease, even in cats who are not showing any symptoms. Ask your vet about SDMA testing at your cat’s next wellness appointment. 

Urinalysis

Urine testing is used to evaluate urine concentration (known as specific gravity), protein leakage, and examine the sediment for signs of infection, inflammation, blood cells, or crystals. A urine sample is generally collected through a quick and easy procedure known as a cystocentesis, in which the vet will insert a small needle through the abdomen and into the bladder. 

Additional Diagnostics

Your veterinarian might also recommend further tests to understand the extent of kidney damage and pinpoint any underlying causes:

  • Blood pressure measurement: High blood pressure (hypertension) is a frequent complication of kidney disease and needs to be addressed for optimal management.
  • Imaging: X-rays can assess kidney size and shape and can sometimes show stones or other abnormalities. Ultrasound gives a detailed look at the kidneys’ internal structure.
  • Urine culture: This test identifies any bacteria causing a urinary tract or kidney infection.
  • Urine Protein Creatinine Ratio (UPCR): Helps quantify the severity of protein loss in the urine.
  • Renal biopsy: In some cases, obtaining a small kidney tissue sample may be necessary for a definitive diagnosis of the specific type of kidney disease.

Staging of Kidney Disease 

Veterinarians use a staging system devised by the International Renal Interest Society (IRIS) to classify the severity of both chronic and acute kidney disease in cats (separate criteria are used for each). Staging is based on creatinine and SDMA levels in the blood, and substaging provides further information based on the presence of protein in the urine and blood pressure measurement. 

Here’s a very simplified summary of the IRIS staging for CKD:

  • Stage 1: Early kidney disease without obvious clinical signs – creatinine may be within the normal range and SDMA may be normal or slightly increased.
  • Stage 2: Mild kidney disease – symptoms may be mild or absent, and creatinine and SDMA levels are often mildly elevated.
  • Stage 3: Moderate kidney disease – symptoms are present and creatinine and SDMA levels are elevated. 
  • Stage 4: Severe kidney disease or kidney failure – creatinine and SDMA levels are high, and the cat is likely to be showing severe symptoms of end-stage disease. 

Why Staging Matters

Staging helps provide your vet with more information about your cat’s kidney disease and inform their next decisions. 

  • Treatment guidance: More severe stages of disease often require more intensive treatments and fluid therapy.
  • Monitoring: Staging lets vets track if the disease is stable, worsening, or improving with treatment.
  • Prognosis: While every cat is different, higher stages generally correlate with a more guarded prognosis, particularly if they don’t respond well to treatment. Detecting kidney disease early, often in the IRIS 1 or 2 stages, offers the best chance for effective management and slowing the progression of CKD.

Treatment of Feline Kidney Disease 

Unfortunately, CKD has no cure, but treatment focuses on slowing its progression, managing symptoms (such as vomiting), and controlling complications (such as high blood pressure). In some cases (especially those of acute kidney injury), an underlying cause may be identified and treated – examples include treating a kidney infection with antibiotics or “unblocking” a cat with a urinary obstruction. Cats who are severely ill often require hospitalization for several days for IV fluids or even hemodialysis if available. 

Diet therapy

Prescription kidney diets for cats are specially formulated to contain reduced levels of protein and phosphorus, which help reduce the workload on the kidneys. Lower protein helps minimize waste product buildup, while controlled phosphorus protects the kidneys from further damage and complications.

Fluids

Fluids are another key aspect of managing kidney disease. In cases of severe dehydration or acute kidney injury, intravenous (IV) fluids can be delivered directly into the bloodstream in a hospital setting, often for several days. Alternatively, subcutaneous fluids can be administered under the skin to help rehydrate cats with kidney disease and support the elimination of toxins. Your veterinary team may teach you how to give these fluids at home.

Medications

Medications are used to help manage complications and clinical signs of kidney disease, and may include: 

  • Phosphate binders: These medications reduce phosphorus absorption from the intestines, helping to maintain healthy blood phosphorus levels.
  • Anti-nausea medications: Nausea and vomiting are common symptoms of kidney disease. These medications offer relief, making your cat feel more comfortable and encouraging better food intake.
  • Appetite stimulants: If your cat’s appetite is significantly reduced, appetite stimulants may be needed to encourage eating.
  • Medications for high blood pressure: Hypertension can damage the kidneys further, or lead to other consequences such as retinal detachment and blindness. Monitoring and managing high blood pressure is an important part of your cat’s treatment plan. 
  • Potassium supplementation: Potassium loss through the urine can be a problem in kidney disease. Supplementation helps maintain healthy potassium levels, which are crucial for bodily functions.
  • Antibiotics: Cats with kidney disease are prone to urinary tract infections. Antibiotics can also treat some underlying causes of kidney disease, such as pyelonephritis. 
  • B Vitamins: These essential vitamins can be depleted in kidney disease. 
  • Treatment of anemia: If your cat develops anemia (low red blood cells) secondary to kidney disease, medications to boost red blood cell production or, in severe cases, blood transfusions may be necessary.

Prognosis and Prevention of Renal Disease

The outlook for cats with kidney disease depends on many factors, including the underlying cause, the severity (stage) at the time of diagnosis, and how well the cat responds to treatment. With ongoing care and monitoring, many cats with CKD can live for years with a good quality of life. Some causes of AKI, such as ingestion of antifreeze or lilies, require emergency treatment yet are often fatal. However, cats who survive the initial incident with appropriate treatment often go on to do well long-term. The best ways to help prevent kidney disease in your cat include regular veterinary checkups (especially for senior cats), providing ample fresh water to your feline friend, and avoiding potential toxins. 

Kidney disease may be part of your cat’s journey, but understanding the condition, recognizing the signs, and partnering with your veterinarian for appropriate treatment are key to helping your cat live the longest, healthiest life possible.

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