By Jason Johnson, DVM, MS, DACT

As veterinary professionals, regularly evaluating kidney health provides information that helps us make more confident care decisions for animals. Not only are kidneys vital organs supporting major systems in the body, but they are also an early detection system and essential pillars of medical assessment for pets.

But could the kidneys be trying to tell us even more about what's going on with our patients?

A robust kidney evaluation—from juvenile to geriatric—should include all reliable screening diagnostics. In addition to creatinine (CREA) and blood urea nitrogen (BUN), symmetric dimethylarginine (SDMA) testing now plays an increasingly important role in diagnostics. The following explores everything you need to know about adopting SDMA testing into your practice and five key patients that could benefit most from this testing.

SDMA testing was launched by IDEXX¹ in 2015, and it revolutionized how the industry monitors kidney health in patients. During that same year, the International Renal Interest Society (IRIS), recognizing the importance of SDMA, changed its staging guidelines for chronic kidney disease (CKD) to include SDMA.

Diagnostics to support patient care

BUN and CREA have been the go-to tests for monitoring kidney health for years. Yet SDMA, which is a kidney biomarker, is more sensitive in detecting renal disease and can do so earlier than these traditional kidney parameters. For example, SDMA increases with an average of 40 percent loss of kidney function, and in some cases, it increases with as little as 25 percent loss of function versus CREA, which does not increase until at least 75 percent of kidney function is lost.^2-5

"I tell my clients that I run SDMA because it allows early detection and early treatment of renal disease, which results in a longer quality of life," says Michael Rose, DVM, owner of the Monticello Animal Hospital in Charlottesville, Va. "It's the test I use when I want to find out early enough to make a difference."

The ability to consistently detect changes to kidney function earlier makes a difference for many patients and may impact diagnosis, treatment, and overall outcomes.

Beyond CKD

As a biomarker, SDMA increases a veterinarian's ability to monitor kidney function and helps accurately detect changes in kidney health.⁶ In addition to CKD, impacts to kidney health can include acute kidney injury, pyelonephritis, glomerulonephritis, upper urinary tract obstruction, kidney stones, and other congenital diseases.^2-4,7-21

Adding SDMA to chemistry profiles for dogs and cats also helps detect earlier changes in other conditions.^2-21 This is because a persistently elevated SDMA concentration indicates a decreased glomerular filtration rate (GFR), identifying the loss of kidney function due to kidney diseases or secondary disease processes that impact kidney function.⁶

For example, adding an SDMA test to blood work can provide a deeper clinical understanding of hyperthyroidism—especially in cats, where SDMA is a more reliable measure of GFR than CREA.^22,23 It can also help catch secondary kidney damage in canine patients that have tested positive for vector-borne diseases and provide critical insight into kidney function for animals with cancer, helping minimize long-term damage while diagnosing and treating the patient.^24,25

SDMA testing can also help veterinary professionals stay ahead of a range of other conditions, such as systemic hypertension, cardiorenal syndrome, lower urinary obstruction, sepsis, and drug toxicity—providing a more robust view of a pet's overall health. ^26-29

Patient profiles that may benefit most

While SDMA testing offers insight and clarity into the health of just about any patient, monitoring changes in kidney function is crucial in the following cases:

• Pets receiving wellness exams. Veterinary professionals know an absence of symptoms does not necessarily equal good health; only diagnostics give us the complete picture. Therefore, SDMA testing should be included in the bloodwork for every patient presenting for a wellness exam. While both dogs and cats benefit from kidney function evaluations, cats have an exceptionally high prevalence of CKD as they age.²⁰
• Cats with hyperthyroidism. Unfortunately, finding a reliable marker for kidney function in hyperthyroidism is not always easy. The hypermetabolic state caused by hyperthyroidism can lead to increased GFR and reduced muscle mass, which makes diagnosing CKD challenging.^22-23,31-34 Because SDMA is less affected by muscle mass, it can be a valuable diagnostic tool for identifying any underlying impact on renal function.³²
• Preanesthetic patients. Ensuring kidney health is vital before anesthesia. Just because a patient seems healthy does not mean underlying conditions could not complicate their anesthesia or a surgical procedure. For preanesthetic profiling, SDMA testing can be an effective way to broaden the assessment of kidney function.
• Infectious and vector-borne disease exposures. With the kidneys being such a central part of systemic health, they are often impacted by infectious diseases. In these cases, SDMA testing can catch declining kidney function early and provide a clinical flag to investigate these diseases in endemic areas.^23,25
• Medical cases. Understanding kidney status can inform diagnostic and clinical decisions in acute and chronic illness cases. For example, if a patient has a primary disease, early identification can help improve the quality and improved longevity. Kidney status can also affect treatment choices and long-term follow-up in a concurrent illness. In either scenario, SDMA testing can add another layer of confidence and understanding to medical decisions, patient care, and communications.

You can explore various SDMA testing options to support your practice and patients, from in-house tests with multiple SDMA-inclusive profiles to a range of options from a reference laboratory. There are also resources to help run the tests, interpret results, and order and implement testing in your practice, along with self-guided sessions to help teams master SDMA testing on their own.

As veterinary professionals, we all want to make a meaningful difference in the quality of our patients' lives. While biomarker tests like SDMA are still relatively new to the veterinary world, not including them in screenings means you could miss out on opportunities to catch diseases early and initiate treatment to help prolong a pet's life.

SDMA testing is a reliable way to check the status of kidney health, elevate your baseline diagnostics, and improve patient care. The kidneys have a lot to say about our patients' health—this is one way to ensure we are able to take action.

Jason Johnson, DVM, MS, DACT, vice president and global chief medical officer at IDEXX, with more than 19 years of experience within the veterinary industry. Dr. Johnson was the co-founder/vice president and dean of LMU-College of Veterinary Medicine, and founder of the Center for Animal and Human Health in Appalachia. He has conducted international veterinary work across seven countries and believes it is both a privilege and a responsibility to elevate animal health around the globe.

References

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