Symmetric Dimethylarginine (SDMA), is a byproduct which results from the enzymatic breakdown of certain proteins. SDMA is normally removed from the bloodstream by healthy kidneys. So, measurement of SDMA concentration in the blood can be indicative of kidney health.
Information about the value of testing continues to evolve. The prevailing opinion among veterinary nephrologists now is that SDMA measurement can be a useful diagnostic tool when utilized along with creatinine measurement, especially in older cats that are losing muscle mass.(1) However, there are caveats:
There is still research to be done: The International Renal Interest Society (IRIS)—the gold standard for CKD diagnosis and treatment guidelines—indicates that the ability of a persistently increased SDMA to predict CKD remains to be seen.(2)
And there are some specific concerns. For example, IRIS notes that SDMA utility may be compromised in cats and or dogs with lymphoma.(3) Also noteworthy is an early research study indicating that SDMA utility may be compromised in cats with diabetes.(4) IRIS also notes that the breed and/or size of some companion animals may affect their SDMA test results. For example, healthy Birman cats often have SDMA and creatine measurements that fall outside of the ranges generally considered normal.(3)
An additional concern expressed to us, by a prominent researcher whose research we have supported, is that SDMA testing may appear to perform better than the standard creatinine test, but that it actually may perform similarly depending on the "cut points" i.e.: the points where normal versus abnormal are defined for each test.
Despite these concerns SDMA testing does continue to demonstrate utility, and IRIS updated it's staging guidelines in 2022, and it’s educational materials in 2023, to reflect the evolving evidence, and they expect to continue doing so as more information emerges. (IRIS states that SDMA assays are offered by numerous laboratories, but that the methodology is not yet standardized, and that their recommendations are based on the IDEXX Laboratories proprietary methodology.)
At this time, it is advisable to obtain both creatinine and SDMA tests for your cats. And please remember, the best chance to catch Feline CKD as early as possible is with regular vet checkups, including bloodwork and urinalysis—see your vet yearly, twice yearly for seniors.
1. Creatinine is a normal by-product of muscle activity, and is normally removed from the body by the kidneys. If muscle is lost, (which often happens in older patients, and in patients with Chronic Kidney Disease), then less creatinine is produced. Therefore, creatinine levels in CKD patients could be falsely low (i.e.: closer to normal) than they would be if muscle mass were normal, thereby giving the impression that they kidneys are functioning better than they really are.
2. https://www.iris-kidney.com/iris-staging-system
3. https://static1.squarespace.com/static/666b9ecb4064a156963b4162/t/66a6dbc90ca6986e1b5c06bd/1722211273243/2_IRIS_Staging_of_CKD_2023.pdf
4. https://pubmed.ncbi.nlm.nih.gov/29230874/
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