Symmetric dimethylarginine and creatinine concentrations in serum of healthy draft horses

BACKGROUND: Symmetric dimethylarginine (SDMA) is considered a more sensitive indirect estimate of glomerular filtration rate (GFR) than creatinine (Cr). Symmetric dimethylarginine is not affected by sex or muscle mass in small animals. OBJECTIVES: To validate a commercial SDMA immunoassay (IA) for equine serum; to compare SDMA and Cr in cohorts of draft horse breeds; and to assess effects of age, sex, and breed. ANIMALS: One hundred and sixty‐five healthy draft horses (0.5‐16 years), including 63 Percherons, 52 Clydesdales, and 50 Belgians. METHODS: Cross‐sectional study. The SDMA IA was validated for equine serum by comparison to liquid chromatography‐mass spectroscopy (LC‐MS) results and other methods. Symmetric dimethylarginine and Cr were compared by analysis of variance and correlation analysis. RESULTS: Median and 95% confidence intervals (CIs) for LC‐MS (10.0 [9.4, 10.2] μg/dL) and IA (9.7 [9.5, 10.0] μg/dL) SDMA concentrations were strongly correlated (R = .74, P < .001). Symmetric dimethylarginine was lower (P < .01) in Percherons and Belgians, than in Clydesdales. Median values and 95% CI for Cr were 1.3 (1.2, 1.4), 1.4 (1.3, 1.5), and 1.4 (1.3, 1.5) mg/dL (P = .06) for Percherons, Clydesdales, and Belgians, respectively. Symmetric dimethylarginine was correlated to Cr (LC‐MS, R = .60, P < .001; IA, R = .66, P < .001). There were no differences in SDMA or Cr between sexes and there were no correlations between age and SDMA or Cr. CONCLUSIONS AND CLINICAL IMPORTANCE: Although a significant breed effect on SDMA concentration was found, differences were small and all medians were <14 μg/dL, the cutoff value to support renal dysfunction in dogs and cats.