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.