During the IDEXX Sunrise Session at the 2019 AAEP Convention, Rana Bozorgmanesh, BSc, BVetMed, DACVIM, MRCVS, presented information on using symmetric dimethylarginine (SDMA) as a diagnostic test in neonatal foals and mares.
SDMA (symmetric dimethylarginine) is a novel kidney test that has recently been enabling veterinarians to diagnose kidney disease earlier than traditional diagnostics in dogs and cats. It has been shown to increase in both acute kidney injury (AKI) and chronic kidney disease (CKD). SDMA is also specific for kidney function and has been shown to be less impacted by extrarenal factors, including body condition, advanced age, and disease state. Because of the advantages SDMA brings for assessing kidney function, IDEXX has been investigating its use in other species, including horses.
According to IDEXX, SDMA has the potential to be a powerful diagnostic tool in horses, especially in situations where a sensitive indicator of kidney function is needed, such as monitoring of at-risk patients during therapy (e.g., equine athletes, geriatric horses on NSAIDs, or septic patients receiving potentially nephrotoxic antibiotics). In order to provide SDMA as a diagnostic option for horses, IDEXX Reference Laboratories took part in two clinical studies. These studies validated the IDEXX SDMA Test in horses and also established reference intervals for equine SDMA. The use of the IDEXX SDMA Test in horses was validated through comparison of results for 178 horses to the gold standard method, liquid chromatography–mass spectrometry (LC-MS). This study confirmed that the IDEXX SDMA Test was able to accurately and specifically detect SDMA in equine blood. Following the validation, a reference interval study on healthy adult horses was performed. IDEXX followed the Clinical and Laboratory Standards Institute (CLSI) guidelines for determining our equine SDMA reference interval. Clinically healthy populations of adult horses of various breeds and sizes were enrolled into the study. Animals characterized as healthy based on history and physical examination were used to establish the reference intervals.
The SDMA reference interval for horses was determined to be 0–14 ug/dL, the same as those seen in dog and cats. NOTE: The is included in the IDEXX equine panels and profiles at no additional charge, and references for the above statements can be found here.
Research Presented During AAEP
Bozorgmanesh conducted this research in conjunction with Drs. Jessica Thornton, Jackie Snyder, Caitlin Fletcher, Katie Offer, Elizabeth Halliwell, Rebekah Mack, Michael Coyne and Nathan Slovis; plus Rachel Murphy and Evan Hegarty.
She noted that SDMA is a methylated form of arginine in intracellular proteins of all nucleated cells. It is released into circulation when these proteins are processed. It is excreted by the kidneys. It is a renal biomarker correlated with glomerular filtration rate (GFR) in humans, dogs and cats.
There are typically four types of neonatal hypercreatininemia: “spurious,” pre-renal, renal, and post-renal; however usually there is some degree of overlap. Spurious hypercreatininemia is associated with placental insufficiency or fetal stress. This condition is common, and usually decreases by more than 50% within 24 hours to normalize within about 72 hours.
Bozorgmanesh noted that there currently are no practical and rapid means of differentiating the underlying causes of hypercreatininemia.
In one study, serum and whole blood samples were collected from mares in their last month of pregnancy and again with their foals around 12 hours, 48 hours, seven days, and 30 days post-birth. A reference range for neonatal foals was established and they demonstrated that neonatal SDMA concentrations are much higher than the adult reference range.
In the second study SDMA concentrations were evaluated in sick, hospitalized neonatal foals. Her hypotheses were that neonatal foals with suspected renal dysfunction have higher SDMA concentrations than foals with creatinine concentrations that rapidly normalize, and that sick, hospitalized neonatal foals have higher SDMA concentrations than healthy foals.
Results from the second study can be summarized as:
- Neonatal foals with suspected renal dysfunction have higher SDMA concentrations than foals with presumed “spurious” hypercreatininemia from 24 hours post-admission to the hospital onwards
- Sick, hospitalized neonatal foals had higher SDMA concentrations than healthy foals at comparable time points
In her discussion, she noted that foal SDMA concentrations were high in both studies throughout the study periods, and she postulated why this may be. She recommended that future studies should include GFR measurement.
Conclusions
Bozorgmanesh concluded that:
- Neonatal SDMA remained higher than the upper limit of the adult reference range during her study periods
- Broodmare SDMA concentrations were slightly higher than the upper limit of the adult reference range around foaling
- SDMA concentrations over time may prove useful to differentiate neonatal foals with hypercreatininemia
- SDMA was significantly higher in sick, hospitalized neonatal foals compared to healthy foals at comparable time points.
About Dr. Bozorgmanesh
Bozorgmanesh studied veterinary medicine at The Royal Veterinary College in London, graduating with Honors in 2008. She also attained an intercalated degree in veterinary conservation medicine from the University of Liverpool during that time. She went on to complete an internship in a large private practice in the UK, then spent four Thoroughbred breeding seasons traveling between the UK, Australia and the Middle East. Afterward she completed a year-long internal medicine fellowship at Hagyard Equine Medical Institute, followed by a large animal internal medicine residency at UC Davis, California, during which time she was awarded The Rowan Fellowship by The California Thoroughbred Foundation for her contributions to research. She stayed on at UC Davis following her residency as Associate Veterinarian in the Equine Internal Medicine Department before moving back to Kentucky.
Her interests include ophthalmology, transfusion medicine, gastrointestinal disease, neonatal medicine and medical management of the critical broodmare. She is currently working on manuscripts regarding rib fractures in equine neonates, fecal transfaunation in adult horses and validation of an equine platelet concentrate; as well as book chapters on Serum Amyloid A, Methemoglobinemia and Heinz Body Anemia.
Bozorgmanesh, who is a Diplomate, American College of Veterinary Internal Medicine, and a Member of the Royal College of Veterinary Surgeons, is a member of the AVMA, AAEP, ACVIM, BEVA, Kentucky Veterinary Medical Association, Kentucky Association of Equine Practitioners, and the Kentucky Thoroughbred Farm Managers’ Club.
