Protein Losing Nephropathy in Cats

PLN develops before the cat’s kidneys go into failure. Because cats are so good at compensating when they are sick, it isn’t easy for the owner to see signs of illness. It’s only when a major percentage of renal function has been lost that obvious symptoms develop.

Protein losing nephropathy (PLN) in cats develops as the result of other, underlying kidney disease. Some forms of PLN are glomerulonephritis, amyloidosis, and glomerulopathy. If the cat has glomerulonephritis, its glomerulus isn’t allowing molecules of creatinine, urea, water and sodium to pass through. Instead, it has become clogged, which creates an inflammation inside the kidney. If the cat has glomerulonephritis, the clogging action develops as a result of an antigen-antibody reaction. 

As the cat becomes ill, it may show the following symptoms:

• Excessive thirst
• Excessive urination
• Loss of interest in food
• Nausea and vomiting
• Water retention
• Dull fur
• Lethargy

Causes of PLN include:

• Feline infectious peritonitis (FIP) 
• Feline leukemia virus (FeLV) 
• Mycoplasmal polyarthritis
• Pancreatitis
• Neoplasia (cancerous growths in the kidneys)
• SLE (systemic lupus erythematosus)
• Diabetes mellitus
• Amyloidosis
• Other diseases of the immune system

For some cats, a cause of PLN can’t be found. These cases are called “idiopathic PLN.” Abyssinian cats are prone to developing amyloidosis, which leads to PLN. In this breed, amyloidosis is inherited, leading to the deposits of amyloid proteins into the kidneys. If the condition reaches this stage, it may be fatal.

Persian cats are at higher risk of developing polycystic kidney disease, which alerts the vet and cat owner to the possibility that chronic kidney disease may follow. 

The vet performs a full physical exam on the cat, looking for symptoms and abnormalities that can direct them in what tests to administer. The vet palpates the cat’s abdomen, which allows them to determine the size and potential sensitivity of the kidneys and bladder. Abdominal palpation also allows the vet to detect abnormal fluid buildup in the cat (this fluid buildup is referred to as “ascites.”) The vet also conducts a digital palpation of the cat’s perineum and rectum, looking for indications that the cat’s lower genital tract and urinary tract are involved as well.

The cat’s blood pressure is measured while the vet is examining its circulatory system. The cat’s eyes should also be checked.

A urinalysis can reveal abnormally high amounts of protein in the cat’s urine. If the cat has a lower urinary tract infection, the abnormal protein reading should resolve once treatment has been completed.

Another diagnostic test is the urine protein/creatinine ratio (UPC). This gives the vet a good reading of the cat’s urine protein excretion over a 24-hour time period. Once the vet has diagnosed PLN, they will run other diagnostic tests to uncover what is causing this condition. These include a CBC, serum chemistry panel, urine culture, feline leukemia testing, and X-rays and ultrasounds to give the vet a good picture of what is happening in the kidneys. Blood testing examines concentrations of blood creatinine, if the vet suspects chronic kidney disease. Another blood test, called plasma albumin concentration, is indicated if the cat has a severe proteinuria caused by glomerulopathy.  Any other diagnostic testing would rely on the individual cause of PLN in the cat.

The cat may undergo a renal biopsy, which is only done if the cat’s coagulation profile and bleeding times are within normal ranges. This test allows the vet to determine the correct diagnosis, the cat’s potential progression through treatment, and its prognosis once the PLN has been resolved. 

Once the vet has diagnosed PLN, they will change, prescribing a food with lower protein levels. decreases the level of protein loss and the levels of protein moving through the cat’s renal tubules. Any protein in the cat’s food should be high-quality.

Next, the vet prescribes and ACE (angiotensin converting enzyme) inhibitor. These work well to lower the levels of protein loss. Potential medications include Enalapril, telmisartan and benazepril. While the cat is taking these medications, the vet should perform regular chemistry panels (blood) for the cat, so azotemia can be detected. Azotemia is an abnormally high amount of creatinine, urea, other nitrogen-rich compounds and body waste compounds in the cat’s blood. This test should start no later than one week after medication therapy has begun. If the cat doesn’t have azotemia, its protein shouldn’t be severely restricted. Feeding the cat between two and three grams of high-quality protein daily is sufficient.

While dogs can take low-dose aspirin as a part of treatment, this should NOT be given to cats. If the cat isn’t azotemic, it can take prednisolone in a gradually decreasing dosage over two or three weeks, especially if the cat’s PLN started as the result of an immune disorder, although this form of therapy is considered controversial. 

If the cat has amyloidosis, dimethylsulfoxide and colchicine can be prescribed, but their results have not been consistent in other cases. In the cat with amyloidosis, corticosteroids should NOT be given.

N3-fatty acids absorb into the renal membranes of the kidneys, so this can be added to the cat’s treatment regimen. These are the precursors of beneficial prostaglandins, which promote the dilation of blood vessels and help to suppress inflammation.

Once a cat has been diagnosed with PLN, its prognosis is usually poor. It may survive, on average, about one month. If it receives ACE inhibitors, its survival time may be extended, as long as it hasn’t begun going into renal failure.

The cat owner needs to maintain the cat on its high-quality, low protein food long-term so it won’t continue leaking protein into its urine after being treated. Any conditions that led to the PLN need to be treated and managed, if they aren’t curable, so the cat can stay fairly healthy.  In addition, the cat’s owner should watch for signs of worsening illness, which could indicate the cat is beginning to go into renal failure.