Kidney test offers hope for cat cases

Old cats get kidney disease, and it typically isn’t diagnosed until it is far advanced.

But presentations last month by Dr. Jane Robertson, Dr. Dru Forrester and Dr. Margie Scherk at the annual meeting of the American Association of Feline Practitioners offered new research findings on early diagnosis and tips on nutritional management of the disease. Typically, cats don’t show symptoms in the early stages of chronic kidney disease. Concentrations of kidney waste products such as blood urea nitrogen (BUN) and creatinine may still be at normal levels.

It’s not until the disease progresses significantly that cats begin to develop physical signs, such as weight loss, decreased appetite, dehydration and excessive water consumption and urination. But a new kidney function test called SDMA, introduced last summer, can identify chronic kidney disease an average of 17 months sooner in cats, according to a study published last year in the Journal of Veterinary Internal Medicine.

Symmetrical dimethyl arginine – you can see why it’s called SDMA – is a form of arginine, an essential amino acid for cats. If you remember your grade-school science class, you know that amino acids are building blocks of protein. As protein breaks down, it releases SDMA into the blood; it’s then excreted by the kidneys. Rising levels of SDMA in the blood are noticeable when only 40 percent of kidney function has been lost, as opposed to higher levels of BUN and creatinine, which may not become evident until 75 percent of kidney function is gone.

Does that mean your cat should get the test? Not necessarily, Scherk said in an email interview. Factors that are known to affect progression and survival, such as proteinuria (protein in the urine), hypertension and anemia, are not detected with SDMA. She adds that dehydration, which is common in cats, may cause artificial elevations of SDMA.

Among the cats who may benefit from the test are thin, older cats with muscle wasting, Scherk says. That’s because those cats may have artificially low levels of creatinine caused by muscle wasting, but SDMA levels aren’t affected by muscle. The test could also be useful for cats with heart disease who may also have early kidney disease that could be worsened by treating the heart disease.

Pet Connection is produced by a team of pet-care experts headed by veterinarian Dr. Marty Becker and Kim Campbell Thornton, author of many pet-care books.