SDMA kidney function test is the newest test for evaluating kidney health in dogs. It has been around for a while now so I figured it’s time to ask veterinarians how they feel about it.
Have you been using the new kidney function blood test [SDMA]? How would you rate its usefulness?
Chronic kidney disease (CKD) is one of the most common chronic ailments affecting dogs and cats. Approximately 33% of cats and 10% of dogs develop CKD over their lifetime, and these numbers likely under-represent the true overall incidence. Although chronic kidney disease is an irreversible and progressive condition, early detection may offer an opportunity to improve both a patient’s quality and length of life. As a veterinarian, I would happily embrace a non-invasive test that allows me to potentially improve a patient’s quality of life through earlier diagnosis and intervention.
The gold standard for evaluating kidney function is the glomerular filtration rate (GFR). Unfortunately, measuring GFR is relatively impractical in a clinical setting. Thus, veterinarians have traditionally based a diagnosis of CKD on clinical signs, changes in urine concentration, and elevations in serum concentrations of creatinine and blood urea nitrogen (BUN). Generally speaking, urine concentration decreases, and serum creatinine concentration increases when 66% and 75% of renal function are lost, respectively. Unfortunately, these parameters have their own limitations. For example, in dogs, increased thirst (called polydipsia) and frequency of urination (called polyuria) are often the first clinical signs of CKD, but cats often initially only manifest polydipsia because they maintain their ability to concentrate urine longer. Creatinine is influenced by muscle mass, and BUN is affected by dehydration, dietary protein content, liver dysfunction, and gastrointestinal bleeding.
In an effort to diagnose CKD earlier, veterinarians have researched a myriad of biomarkers. Symmetric dimethylarginine (SDMA) is a novel biomarker of kidney function correlates more closely to GFR than creatinine or BUN. This biomarker elevates earlier than creatinine, allowing veterinarians to diagnose CKD earlier in the course of disease progression. Research in cats has shown SDMA generally becomes elevated when 40% of renal function is lost. Similar findings have been documented in dogs. Practically speaking, SDMA measurement may allow veterinarians to diagnose CKD 17 months and 9.5 months earlier in cats and dogs, respectively.
Unlike creatinine and BUN, SDMA isn’t influenced by muscle mass or other ailments like liver disease, heart disease, and Cushing’s disease. However, this biomarker isn’t perfect. For example, rarely cats may develop low thyroid hormone levels after radioactive iodine for hyperthyroidism. Research has suggested hypothyroidism may be associated with increased SDMA concentrations due to reduced GFR. The simple fact is this test is relatively new, and continued research is needed to understand all of the factors that may influence this new kidney biomarker. Nevertheless, I encourage my primary care colleagues to incorporate SDMA testing into their preventative healthcare screening protocols, especially in middle-aged and geriatric patients. When interpreted accurately, SDMA offers the possibility of identifying CKD earlier in its course, thus affording veterinarians the opportunity to intervene earlier for the benefit of their patients.
One must be careful to not over-rely on one renal parameter but interpret along with the other blood renal parameters and a urinalysis. If used as part of the picture of renal function I am happy with the information. If used as the sole parameter in decision making it frequently leads people astray.
Yes, I have been using the new kidney function test (SDMA). The test now comes as a component of the routine blood testing I do on my canine and feline patients through IDEXX laboratories. SDMA is slated to help detect kidney disease before other blood values that are conventionally assessed to determine kidney health (blood urea nitrogen, creatinine, phosphorus, etc.) become abnormal.
Although I have had some variable results, it’s has been helpful in giving me a better assessment as to my patient’s kidney function. By variable results, I mean that I have had patients with known kidney disease have normal SDMA values.
Therefore, to fully assess my patients’ kidney health through laboratory testing I look at all available blood values in combination with urine testing such as urinalysis, urine culture, protein to creatinine ratio, etc.
The SDMA test allows veterinarians to detect kidney disease earlier than we could with typical chemistry results. I find it a very useful test.
As part of a complete panel, the SDMA test is a valuable tool to aid us in the diagnosis of early kidney disease. As with any screening test, the results must be evaluated in the context of the patient and the physical examination and clinical pathology profiles available. Kidney disease is often chronic and progressive. Early detection allows for early intervention and the best prognosis for a higher quality of life and increased life span.