Analytical validation, reference interval determination, and diagnostic performance of plasma symmetric dimethylarginine in cattle

BACKGROUND: The efficacy of serum urea and creatinine concentrations in the diagnosis of kidney disease in cattle is limited because of their low sensitivity and specificity. Serum symmetric dimethylarginine (SDMA) concentration is correlated with glomerular filtration rate and has been reported to be useful for the diagnosis of kidney disease in other species. HYPOTHESIS/OBJECTIVES: Test the hypothesis that SDMA may be an effective biomarker for diagnosing kidney disease in cattle. The objectives were to assess the analytical performance of SDMA measurement using a benchtop analyzer to establish an SDMA reference interval in cattle, and to evaluate the efficacy of plasma SDMA concentration for the diagnosis of kidney disease in cattle. ANIMALS: A total of 199 healthy animals (53 male and 96 female beef cattle and 50 female dairy cows) and 27 azotemic cows with confirmed kidney disease. METHODS: A partial analytical validation of SDMA measurement using bovine plasma was performed including assessments of short- and long-term imprecision, linearity, and stability. The reference interval was established following American Society for Veterinary Clinical Pathology (ASVCP) recommendations. Finally, the diagnostic efficacy of SDMA was assessed by determination of specificity, sensitivity, and the area under the receiver operating characteristic curve. RESULTS: The SDMA measurements showed acceptable analytical performance. The reference interval was 60-160 μg/L. No significant differences were found according to sex, breed, or food supply. Using the upper limit of the reference interval (160 μg/L) as the cut-off, sensitivity and specificity were 0.85 and 0.98, respectively. CONCLUSIONS AND CLINICAL IMPORTANCE: An SDMA cut-off of 160 μg/L shows promise for diagnosing kidney disease in cattle, but requires confirmation in future studies.