Evaluation of serum symmetric dimethylarginine as a renal biomarker in Asian elephants (Elephas maximus)

Abstract

Symmetric dimethylarginine (SDMA) has been reported to be potentially more sensitive in identifying renal impairment than blood urea nitrogen and creatinine in dogs and cats. SDMA has been evaluated in multiple domestic and zoologic species but has not been previously evaluated in Asian elephants (Elephas maximus). The objective of this study was to determine if there is a positive association between serum SDMA and creatinine in Asian elephants, calculate normal population-derived reference intervals for a point-of-care analyzer and a reference laboratory analyzer, and determine if SDMA values are elevated in Asian elephants with histopathologic evidence of renal disease. Serum SDMA was analyzed from managed elephants in OK (n = 30) during routine clinical evaluations and from elephants with histopathologic evidence of nephropathies, including nephritis, renal fibrosis, or urolithiasis (n = 10) by reviewing medical records or analyzing frozen serum samples. There was a poor correlation between SDMA and creatinine irrespective of the method (R = 0.02–0.22). The normal reference interval for SDMA with the reference laboratory analyzer in healthy Asian elephants was 4.1–10.9 µg/dl, and it was 6–16 µg/dl using the point-of-care analyzer. Elephants with clinically significant histopathologic nephropathies (4 of 10) had SDMA values between 7 and 23 µg/dl, with only two of four exceeding the upper limit of the reference interval for the reference laboratory analyzer. These results suggest that SDMA may not be a sensitive indicator of renal function in Asian elephants.