By William E. Feeman III, DVM
For more information on SDMA in an easy toread format, please visit:The kidneys are a complex pair of organs that serve many functions in the body.These functions include, but are not limited to, conservation of water, formation of urine,electrolyte balance, and acid-base regulation. Kidney disease or dysfunction could thusresult in an inability to perform one or more of these functions. Clinical signs of kidneydisease include increased drinking, increased urination, vomiting, diarrhea, dehydration,anorexia, weight loss and lethargy.
Kidney disease can be diagnosed in manyways, but bloodwork is the most common methodused. The two main parameters used to judge kidneyfunction on a blood test include the Blood ureanitrogen (BUN) and creatinine levels. Diagnosingkidney disease can be difficult because both BUNand creatinine levels can also be elevated withdehydration or urinary obstruction. In order for theBUN and creatinine to be elevated due to kidneydisease, 75% of the kidney function must becompromised. Therefore, if 74% of the kidneyfunction was lost, the BUN and creatinine may still be normal. In July of 2015, a new bloodtest (SDMA) was released by IDEXX laboratories and it claimed to diagnose kidney disease1-2 years earlier than BUN and creatinine. Initially, it was believed that Greyhounds hadlevels similar to other dogs. Clinically it has been found that some Greyhounds can havemild increases in SDMA while still having normal kidney function. Research is currentlybeing conducted to better define a normal range for Greyhounds. Phosphorous is anelectrolyte in the blood that is often elevated in more advanced stages of kidney disease.An elevation of phosphorous in conjunction with elevations in BUN, creatinine and SDMAwould make true kidney disease significantly more likely.
Dr. William Feeman III DVM
A urinalysis can also be used to help in the diagnosis of kidney disease. The kidneysconcentrate the urine and are responsible for reabsorbing water out of the urine. Elevatedprotein levels in the urine can be indicative of either kidney disease (Glomerular disease)or inflammation of the bladder. A urine protein: creatinine ratio (UPCR) test can be doneto help determine the source of the urinary protein. An elevated UPCR is often indicativeof kidney disease. The urine specific gravity (USG) measures the concentration of the urineand aids in the diagnosis of kidney disease. The kidneys lose the ability to concentrateurine when 66% of the kidney function is lost. Urine specific gravities greater than 1.020are considered adequate and indicative of functioning kidneys. An increase in drinking water (polydipsia) can result in a low USG and therefore be indicative of diseases unrelatedto the kidneys. As a result, a low USG is found in most cases of kidney disease but a lowUSG is not always diagnostic for kidney disease. It is also critical that the USG is measuredfrom a refractometer. The USG found on many urine sticks is very inaccurate.
The final diagnostic steps that can be used to aid in the diagnosis of kidney diseaseare x-rays (radiographs) and an ultrasound. Radiographs will allow the veterinarian tolook for kidney stones and evaluate the shape and size of the kidneys. Abnormally largeor small kidneys are a strong indicator of kidney disease. An ultrasound further allows theveterinarian to evaluate kidney structure and architecture. In rare cases, an ultrasoundguided biopsy of the kidney may be taken for a definitive diagnosis.
Treatment options for kidney disease can vary widely based on the diagnosis. Asimple change in diet is recommended for mild cases, while intensive hospitalization,intravenous fluids and possible surgery may be recommended for more severe cases.
The complicating factor in the diagnosis of kidney disease in Greyhounds is thatGreyhounds run a significantly higher BUN and creatinine than other breeds (exact valueswill vary by the laboratory used). Many Greyhounds will have high normal or just abovenormal BUN and creatinine values, yet their kidney function is completely normal. If yourveterinarian is suspicious of kidney disease based on only mild elevations in bloodwork, askhim/her to run a urinalysis and to check the USG using a refractometer. If the USG is >1.020then the elevations in bloodwork are unlikely to be from kidney disease, but from anothersource. In this example, the values are suspected to be normal for a Greyhound. If theurine specific gravity is low, it may be worth rechecking it on another sample to verify if thelow level is repeatable. Ideally try to check the first urination of the day as this tends to bethe most concentrated sample. If your Greyhound is asymptomatic but has elevations inBUN, creatinine and SDMA and has dilute urine, I would recommend rechecking thebloodwork in another 4-6 weeks to ensure the values are not worsening. Elevating valuesover this time period would be indicative of kidney disease and appropriate treatment shouldbe discussed with your veterinarian.
To learn more about SDMA and to share with your veterinarian
Veterinarians usually look at your pet's BUN at the same time they consider its creatininelevel. The two values will go up or down in tandem when kidney or urinary tract problemsare the cause and so the ration between BUN and creatinine should remain similar. Whenone is out of balance with the other, health problems outside of the kidney may be theunderlying problem.
SDMA - With the introduction of SDMA by IDEXX (Symmetric dimethylarginine), a testfor renal disease, veterinarians will now have a more efficient and earlier means ofdetecting and diagnosing kidney issues. SMDA is a renal biomarker, excreted by thekidneys and more accurately reflects glomerular filtration rate (GFR) in dogs and cats.According to IDEXX, “SDMA is also not affected by lean body mass, making it more reliablefor assessing kidney function in animals with chronic kidney disease or other conditionsthat result in weight and muscle loss, such as hyperthyroidism”.
The SDMA test should be run alongside creatinine, BUN, and a urinalysis to helpdiagnose kidney disease earlier and with more confidence. SDMA has been shown to bea much more sensitive indicator than creatinine, which will help veterinarians to identifyacute and chronic kidney injury earlier than ever before. As stated by IDEXX, “SDMA is a more reliable tool to evaluate kidney function and its results should be considered first,before creatinine. However, creatinine is still complementary to SDMA for evaluatingkidney function. A complete kidney evaluation should consist of a thorough history,physical examination, and evaluation of a minimum database, including CBC, chemistryprofile with the IDEXX SDMA Test and electrolytes, and complete urinalysis”. When kidney dysfunction or disease is suspected in your pet, please don’t hesitate to discuss this test with your veterinarian
All of these tests taken together, and separately, give you and your veterinarian accurateindications of kidney disease or injury. The SDMA Test algorithm provided by IDEXXbelow, along with the lab results, give guidance to your veterinarian in deciding theappropriate actions and treatment options for your pet.
IDEXX/SDMA
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