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Your veterinarians has traditionally relied on your pet’s blood urea nitrogen levels (BUN) and blood creatinine levels to judge the health of its kidneys. As the wear and tear of time or specific disease decrease the efficiency of your pet’s kidneys in cleansing its blood, the amounts of those two waste products tend to rise in the blood stream. However, neither begins to rise until the pet's kidneys have lost over half of their original filtering (cleansing) power. Once any of the kidney glomeruli responsible for that filtrating have been lost, there is no known treatment that will bring them back.
So both veterinarians and physicians have been interested in finding other tests that catch the problem earlier that the BUN and Creatinine tests. The urine microalbinuria test was a recent addition that, it was hoped, would detect earlier kidney problems. 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) hopes to get around those drawbacks. It measures the level of Symmetric dimethylarginine in your pet’s blood. That compound (called a biomarker) is formed as the cells throughout your pet's body metabolize and rearrange their protein content. It has no known positive function in your pet’s body and is excreted in its urine. When your pet’s kidneys begin to loose 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) begins to rise. So the test is thought 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 tests pick it up. 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.
Your veterinarian will want to investigate further. He/she will ask if your pet seems to be drinking more water and urinating more than it once did. If the kidneys feel smaller, lumpier or harder than they should. If the kidneys are of equal size. The age of your pet is quite important as well. There is a normal loss of kidney filtering power as we all age – our pets included. Urine needs to be examined for evidence of bacterial infection. Tests might be run to see if the pet was exposed to leptospirosis. A complete blood chemistry might be indicated to be sure there are no underlying diseases that might be causing kidney damage. Diseases like diabetes, hyperthyroidism or Cushing’s disease. Its blood pressure will be checked. The pets exposure to possible toxic substances will be reviewed – things like NSAID (Rimadyl etc.) use, specific kidney-toxic antibiotics or drugs used to fight cancer. A urine bacterial culture might be indicated. It might be x-rayed for possible urinary tract stones.
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. (ref). People have looked for ways to slow or stop the aging process throughout recorded history. To the best of my knowledge, they haven't found any methods yet that work; but that doesn't stop folks from spending $50 billion yearly trying to. (ref) Your pet's are in the same boat. If your pet's blood creatinine is in the upper ranges of normal or above that, the SDMA test confirms that your pet's kidneys have lost some of their blood-cleansing abilities. But it adds no treatment options to age-related kidney decline that pets and humans didn't already have. Those options are at best, minimally effective.
There are genetic lines of purebred cats and dogs that are potentially carriers of early kidney failure (polycystic and multicystic kidney disease). (ref1, ref2). The SDMA test is one way we can screen these animals for genetic kidney problems while they are young before placing them in a breeding programs. (ref)
If your veterinarian other examinations identify disease processes that may be affecting your pet’s kidneys, those need to be cured, treated or stabilized. (Results tend to be slightly higher in growing puppies and kittens and in greyhounds.)
But in many cases no specific cause for a high SDMA reading will be found. As I mentioned earlier, nothing we have now will restore lost kidney function.
The veterinary marketplace is full of products and diets that are sold to improve “kidney health” or to furnish “kidney support” - everything from stem cell therapy to Chinese herbals. A great many of these products make claims that are scientifically unsupported. 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 blood and other tests identify uremic signs like chronic anemia, high blood phosphate and perhaps potassium levels or lower than normal calcium need to be addressed with medication and nutritional modification. But we really do not know if giving them before these problems occur is of any real value.
Insuring that your pet gets a maximum amount of water to keep its kidneys “flushed out” is always a good idea. Dry pet foods never encourage sufficient water intake. Pets with known kidney problems need extra care when given anesthesia or placed under stress of any kind. Boarding pets when there is evidence of kidney problems is rarely if ever a good idea.
Once the level of phosphate in your pet’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 the 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 (ref). But a recent study in cats did not find that they improved kidney function in older cats. (ref) Findings were similar in some older studies in dogs (ref1, ref2)
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.
How advisable it is to give those diets to pets based only on an elevated SDMA reading also remains unknown.
The SDMA test for pets only became available to US and Canadian pet owners in 2015. Idexx announced plans to offer it in Europe starting January, 2016. As veterinarians become more familiar with interpreting test results and follow specific cats and dogs over time, recommendations will most certainly be modified.
Some decreases in kidney function that could elevate your pet's SDMA levels are part of the normal aging process. They occur in humans as well. (ref) We do not know yet at what SDMA level it might be wise to begin giving pets medications such as those that increase blood flow through its kidneys (eg Semintra®) . If your pet's blood pressure is above normal, they are indicated. But what if that has not yet occurred ? We just do not know.
The test will have more utility once Idexx makes available SDMA values in specific pet age brackets and reports back in which percentile of an age bracket your pet's results fall.
This is an interactive article. Keep me posted on how your pet with elevated SDMA does over time, on and off medications, and you will be adding to our knowledge bank.
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 run FreeT4 for hyperthyroidism