= Symmetric dimethylarginine

Ron Hines DVM PhD

 SDMA Kidney Test – What It Means – What It Doesn’t Mean  

 Kidney Disease – Its Diagnosis And Treatment 

  Might My Cat Or Dog Need A Special Kidney Diet?  

Your veterinarian has traditionally relied on your dog or your cat’s blood urea nitrogen level (BUN) and its blood creatinine level to judge the health of your pet’s kidneys. As the wear and tear of time, or a specific disease, decrease the efficiency of your pet’s kidneys in cleansing its blood, the amounts of those two waste products will rise in its blood stream. However, neither begins to rise until your pet’s kidneys have lost over half of their original filtering (cleansing) capacity. Unfortunately, once the microscopic kidney glomeruli that are responsible for that filtrating have been lost, there is no known treatment that will bring them back – in pets or humans.

So, both veterinarians and physicians have been interested in finding other tests that might catch the problem earlier than the BUN and Creatinine tests. The urine microalbinuria test was a recent addition. It was hoped that that test would detect kidney problems earlier.  It does detect them earlier. But it can be positive for a number of reasons other than kidney damage. The SDMA test that was recently made available to veterinarians (in 2015), hoped to get around those drawbacks. It measures the level of symmetric dimethylarginine in your pet’s blood. That compound (called a biomarker) is formed when cells throughout your pet’s body metabolize and rearrange their protein content. It has no known positive function in your dog or cat’s body, so it is excreted in its urine. When your pet’s kidneys begin to lose their abilities to excrete it, the level of SDMA in your pet’s blood will go up. That rise occurs before the pet’s blood creatinine and blood urea nitrogen (BUN) begin to rise. So, the test is thought to be able to identify kidney problems earlier – perhaps when as little as 25 – 40% your pet’s kidney function has been lost. Perhaps about a year before the other two tests identify kidney damage. Veterinarians tend to regard a rise in your pet’s blood creatinine level as more serious than a moderate rise in its BUN. However, lean pets do not produce as much creatinine as those with adequate muscle mass and because of that, creatinine level may not accurately reflect the true seriousness of your pet’s kidney problem. The SDMA test is said to not have that drawback.

What If My Dog or Cat’s SDMA Test Results Are High?

Your veterinarian will want to investigate further. He/she will ask you if your pet is drinking more water and urinating more than it once did. The vet will check if your pet’s kidneys feel smaller, lumpier or harder than they should. That is a sign of scarring. The kidneys should also be of equal size. Your pet age is very important as well. There is a normal loss of kidney filtering power in all of us as we age – our dogs and cats included. Your pet’s urine also needs to be examined for evidence of a bacterial infection. Tests might be run to see if your pet was exposed to leptospirosis. A complete blood chemistry profile would be indicated to be sure there are no underlying diseases that might be causing kidney damage. Diseases such as diabetes,   hyperthyroidism in cats or Cushing’s disease in dogs also affect the kidneys. Your cat and dog’s blood pressure will be checked as well. Possible exposure to toxic substances will be reviewed. Medications such as NSAID drugs (e.g. Rimadyl®, Previcox®, Metacam® etc.) can affect the kidney. Other medications with possible negative effects on the kidneys are aminoglycoside antibiotics such as gentamycin and drugs used to fight cancer. It might be suggested that your pet be x-rayed for possible urinary tract stones (calculi). Read about them here.

Should I Be Worried?

If the follow-up tests were normal and your pet is getting on in years, I want you to understand that it is normal for there to be some loss of kidney function as we and our pets age. People have dreamed of ways to slow or stop the aging process throughout history. None have been found, but that doesn’t stop folks from spending $50 billion yearly trying to. (read here) Veterinarians and pet owners are not immune to this temptation either.  If your pet’s blood creatinine is in the upper ranges of normal or above that, the SDMA test does nothing more than confirm that your pet’s kidneys have lost some of their blood-cleansing abilities. It adds no treatment options that veterinarians didn’t already have. Those options are, at best, moderately effective. If beginning your dog on prescription “kidney health” diets earlier due to high SDMA test results increases its lifespan has never been scientifically proven. 

Where Might This Test Be Most Valuable?

There are lines (families) of purebred cats and dogs that are potential carriers of genetic defects that lead to early kidney failure (polycystic and multicystic kidney disease). (read here) The SDMA test is one way we might screen these animals for genetic kidney problems while they are young – before placing them in breeding programs. 

What Are My Options If My Pet’s SDMA Test Results Remain High?

If your veterinarian’s other examinations identify disease processes that may be affecting your pet’s kidneys, those need to be treated or stabilized. But in many cases, no specific cause for the high SDMA reading will be found. SDMA test results tend to be slightly higher in growing puppies, kittens and greyhounds.

As I mentioned, the veterinary marketplace is full of products and diets that are sold to improve “kidney health” or to furnish “kidney support” or to be “kidney friendly” – everything from stem cell therapy to Chinese herbals. Many of these products make claims that are not scientifically supported. Will eating jellyfish make you smarter? (read here) Even those that are scientifically proven to help pets deal with kidney failure (uremia = azotemia) have not been proven to slow the development of uremia. Once your veterinarian’s blood tests identify uremic signs in your pet such as chronic anemia, high blood phosphate and perhaps high potassium levels or lower than normal blood calcium they need to be addressed with medication and nutritional modification. But we really do not know if giving medications or diet modifications before these problems occur are of any value.

Insuring that your pet gets a maximum amount of water to assist its kidneys in “flushing out” toxins is always a good idea. Dry pet foods never encourage sufficient water intake. Pets with known kidney problems need extra care when given anesthetics or placed under stress of any kind. Boarding pets when there is evidence of kidney problems never a good idea.

What About Restricting The Amount Of Protein In My Dog And Cat’s Diet Based On Elevated SDMA Results?

Once the level of phosphate in your dog or cat’s blood rises to above normal levels, excessive protein consumption is unwise. These are probably pets with SDMA values at or above 30ug/dl, although the decision must consider your pet’s creatinine level as well. However, abnormally low protein consumption causes muscle wasting and weakness and diets with high carbohydrate content can have other unwanted effects. Diets low in protein (and fat) can be especially dangerous for cats.
So now, most of the diets sold by veterinarians for pets with evidence of kidney disease have lowered their protein contents to “moderate” levels, not low levels. They also include a variety of ingredients that might, perhaps, be helpful to stem inflammation, and they are low in phosphorus and salt. But a recent study in cats did not find that they improved kidney function in older cats. Findings were similar in some older studies in dogs. Whether those kidney diets might slow the progress of kidney loss in your dog or cat remains unknown and probably will remain so. That is because the types of studies required to judge the long-term value of these diets are no longer permitted due to animal welfare considerations. They would also be quite difficult to fund because the companies that produce these diets see no need to do so. 

Complementary Tests That Come To Mind:

Urine specific gravity,   BUN,   Creatinine,   PCV,   blood pressure,   blood glucose,   cortisol:creatinine, urine microalbuminuria,   urinalysis, blood electrolytes,   phosphorus and calcium level,   anion gap. In older thin cats, FreeT4 for hyperthyroidism

DxMe

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