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