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What Is Proteinuria in Cats?

Proteinuria occurs when there is too much protein in your cat’s urine. While some protein in feline urine is normal, high levels that don’t drop normally can be a sign of an underlying health issue.

Like other mammals, a cat’s urine is first formed in the kidneys, where blood is filtered through a special filtration system. This filtration removes toxins and other byproducts of metabolism, including proteins. A structure in the kidneys called the glomerulus is part of this filtration system. One of its jobs is to prevent larger proteins, like albumin, from exiting the body in the urine.  

Proteinuria may be a sign that the kidneys are not functioning normally and allowing larger proteins to mix into the urine. Excessive protein in a cat’s urine—even on routine urine testing—warrants further investigation to identify what’s causing it. The earlier the cause of proteinuria is determined and treated, the more likely a positive outcome.

Symptoms of Proteinuria in Cats

There are usually no clinical signs of proteinuria in cats. It is often diagnosed during routine, annual health examinations, where bloodwork and urine samples are routinely tested. Symptoms are usually the result of the underlying cause of the proteinuria and not the proteinuria itself.

If symptoms are present, they may include:

  • Blood in the urine

  • Straining to urinate

  • Frequent, small urinations

  • A strong odor to the urine

In more severe cases caused by underlying chronic kidney disease and/or kidney failure, symptoms may include:

  • Lethargy

  • Decreased appetite or loss of appetite

  • Vomiting

  • Increased thirst

  • Increased urination

  • Lack of urine production

  • Edema (swelling of the limbs)

  • Ascites (fluid in the abdomen)

If your vet finds high levels of protein in your cat’s urine, or levels that remain high for too long, they will likely order additional testing. 

Causes of Proteinuria in Cats

Bleeding or inflammation in the urinary tract are the most common causes of protein in cat urine. Usually, this is caused by inflammation in the lower urinary tract (bladder and urethra). Less commonly, the prostate gland, uterus, or vagina may also contribute.

Inflammation or bleeding in the lower urinary tract is most often due to:

  • Urinary tract infection (UTI)

  • Urinary tract stones (kidney, bladder, or urethral)

  • Crystals in the urine

  • Feline idiopathic cystitis (FIC)

Other less-frequent causes of protein in urine include:

Diagnosis and treatment of these underlying conditions usually resolves the proteinuria.

If the protein in your cat’s urine is not associated with inflammation or bleeding, then kidney disease or other systemic diseases may be the cause. Your vet will perform additional diagnostic tests to identify kidney disease.

Other chronic and concerning causes of proteinuria include:

  • Hypertension (elevated blood pressure)

  • Hyperthyroidism

  • Tick-borne disease

  • Diabetes

  • Parasites

  • Toxins

  • Cancers

  • Viruses

  • Any systemic immune-mediated or inflammatory condition

  • Chronic renal disease/renal failure.

Chronic causes of proteinuria require long-term or even lifelong treatment to lessen the protein in the urine.

How Vets Diagnose Proteinuria in Cats

Vets usually first diagnose proteinuria through urinalysis. This test is conducted on a simple urine sample. During the exam, your vet will collect a urine sample with a dipstick and evaluate sediment.

Urinalysis measures the amount of protein in the urine while also assessing for blood and any causes of inflammation, such as crystals, bacteria, and casts (tube-shaped particles made up of cells, protein, or fat).

If more testing is needed, the standard method to obtain urine is called a cystocentesis. For this common procedure, your veterinarian inserts a needle directly into your cat’s bladder to obtain a urine sample. The process is often guided by ultrasound and produces the most sterile sample.  This sample is then sent to the lab for a general urine profile or urinalysis.

If urinalysis reveals blood or inflammation, your veterinarian will likely recommend further testing, including:

  • Urine culture to look for infection

  • Abdominal x-rays to look for bladder/urethral stones

  • X-rays or ultrasound to look for reproductive or prostate disease

After your cat receives appropriate treatment, your vet will repeat the urine testing to monitor for persistent proteinuria.

If elevated protein appears in the urine sample without signs of inflammation or bleeding, then your vet will conduct further diagnostic testing to investigate kidney disease and other systemic causes.

This may include full bloodwork to assess kidney function and protein levels as well as a urine protein/creatinine ratio (UPCR) test. Often, your vet will take your cat’s blood pressure to rule out high blood pressure

If the cause remains unknown, your veterinarian may discuss more thorough tests, such as abdominal ultrasound, infectious disease testing, or viral testing.

Kidney biopsy, which is used to diagnose glomerular disease, is widely considered a last resort. Kidney biopsy is an aggressive, invasive diagnostic test with the potential for significant complications. It is usually performed via abdominal surgery with ultrasound guidance or with a minimally invasive laparoscope. 

Treatment for Proteinuria in Cats

Once your vet figures out what is causing your cat’s proteinuria, they will prescribe the best course of treatment. Treatments vary depending on the cause.

  • Urinary tract infections are often treated with antibiotics and have an excellent chance of recovery.

  • Inflammation of the bladder without infection (feline idiopathic cystitis) is typically treated with anti-inflammatories and pain medications.

  • Bladder crystals can be treated with diet changes and increased water intake.

  • Bladder stones are usually dissolved via diet change or are surgically removed from the bladder via a procedure termed cystotomy. 

  • Polyps in the bladder often can be surgically removed via bladder surgery or cystoscopy.

  • Treating and controlling diseases such as hypertension, hyperthyroidism, pancreatitis, and diabetes may reduce lessen or even resolve proteinuria in cats.  

  • Kidney disease or kidney failure treatment depends on the severity of the disease.

The goal of therapy in cats with kidney disease is to decrease the proteinuria by more than 90%, which may not be possible if the disease is severe.

Treatment may include only a diet change to a low-protein, low-phosphorus diet in the early stages of kidney disease. As the disease progresses, fluid may be administered under the skin. You can be educated on how to perform this therapy at home.

In more severe cases of renal failure, hospitalization with IV fluids may be recommended to correct dehydration, administer electrolytes, and flush/cleanse the kidneys to help lower kidney enzymes and support overall health.

Recovery and Management of Proteinuria in Cats

Most cats with proteinuria caused by acute inflammation or bleeding have an excellent chance of recovering. While they are at risk for recurring urinary issues in the future, they often recover completely with therapy.

Cats with renal disease are often placed on a lifelong prescription diet with low protein and phosphorus. Sometimes, your vet may also prescribe probiotics or kidney supplements (especially omega-3 fatty acids). It is important to discuss any supplements with your veterinarian before giving them to your cat.

Subcutaneous (under-the-skin) fluid administration at home can be helpful in maintaining hydration levels, providing electrolyte support, and flushing the kidneys. Your veterinarian can educate you on how to perform this therapy at home, including which types of fluids to use, how much to administer, and how frequently to do it.

In cases of urinary tract neoplasia, or cancer, surgery and chemotherapy are often used to achieve remission and improve quality of life. Unfortunately, most types of cancers in the urinary tract are aggressive, and even with treatment, they are not usually cured.

Chronic kidney disease is usually monitored closely with frequent visits to the vet for examination, weight checks, blood work, urinalysis, and urine protein creatinine ratio and blood pressure testing to help track any improvement and monitor the disease.

When the disease progresses, oral medications can help support the kidneys, including angiotensin-converting enzyme inhibitors (ACE inhibitors). Your vet may also prescribe immunosuppressive therapy or anticoagulants, depending on the cause and severity of the kidney disease. 

Proteinuria in Cats

What does high protein in cat urine mean?

Proteinuria means there is too much protein in your cat’s urine. Persistent and excess protein levels in the urine are abnormal and usually have an underlying cause. Your veterinarian will investigate what is causing the proteinuria and determine the best treatment options for your cat.

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