Serum Creatinine, Cystatin C and Symmetric Dimethylarginine Concentrations and Relationship Between Them in Healthy Small and Miniature Dogs: A Preliminary Study

Currently, there are common reference intervals for creatinine levels in dogs, despite different weight categories. This can result in missing the diagnosis of kidney disease at an early stage in small dogs. The aim of this study was to determine and compare available markers of the GFR (serum cystatin C, creatinine and SDMA) in healthy small and miniature dogs. Each dog underwent the same protocol, including physical examination, blood pressure measurement and ultrasound of the urinary system. The serum filtration markers determined in the study were creatinine, cystatin C and SDMA. Urinalysis was performed, including urine specific gravity (USG) and the urine protein/creatinine ratio (UPC). Forty samples were included. The median values with the IQR (interquartile range) for creatinine, SDMA and cystatin C levels in the examined dogs were 63.8 µmol/L (16.7), 10.63 µg/dL (4.64) and 0.5 mg/L (0.2), respectively. Compared with Yorkshire Terriers and Chihuahuas, Maltese dogs had significantly higher median serum creatinine concentration (<i>p</i> < 0.001). Combining results of GFR markers, USG, UPC, patient's clinical condition as well as the breed is mandatory when assessing renal function in small dogs. Maltese dogs may have physiologically higher serum creatinine levels.