Comparison of serum creatinine, cystatin C, symmetrical dimethylarginine and resistive index parameters in geriatric dogs

Geriatrics is associated with a gradual deterioration in the balance between organs and systems. In this study, the changes in serum creatinine, cystatin C, symmetric dimethylarginine and resistive index parameters and their relationships with each other were investigated in geriatric dogs. The study material consisted of 41 geriatric dogs (9.41±0.27 years old), 23 males and 18 females, randomly selected, clinically healthy, non-dehydrated and free of chronic diseases. There was no breed and sex restriction in the study. After general examination, blood samples were collected for haemogram and biochemical investigations. Creatinine, cystatin C and symmetric dimethylarginine levels in serum samples were evaluated by enzyme-linked immunosorbent assay. Ultrasonographically, left kidney cortex-medulla ratio was recorded. The resistive index value was measured by doppler ultrasonography at the level of the left renal arcuate artery in all dogs. As a result of the statistical analysis, a high positive correlation was found between serum symmetric dimethylarginine and cystatin C concentrations (p<0.05), while no correlation was found between serum creatinine and symmetric dimethylarginine, cystatin C and resistive index parameters. Similarly, there was no statistically significant difference between renal cortex/medulla ratio and other parameters. However, the mean serum creatinine, cystatin C and symmetric dimethylarginine values measured in the dogs constituting the material were within the reference range. The calculated mean resistive index value was above the reported reference range. As an important result of the present study, the fact that no increase in the mean concentrations of the analysed biochemical biomarkers was observed indicates that the geriatric dogs probably did not develop a severe age-related loss of renal function or renal failure. Creatinine increase has high specificity in renal injury. However, its effectiveness in early diagnosis is limited. On the other hand, it is now generally accepted that cystatin C is a better biomarker than creatinine in the early diagnosis of chronic kidney injury. Symmetric dimethylarginine has been shown to increase in the early period in possible renal damage. In this study, the fact that no change was observed in the measured mean concentrations of cystatin C and symmetric dimethylarginine, which have the potential to increase especially in the early period of renal damage, was considered as a possible indicator that a serious loss of renal function did not develop in the geriatric dogs constituting the material. Whereas creatinine increases only in the presence of significant renal damage, symmetric dimethylarginine and cystatin C may increase early in relation to age-related relative loss of renal function. In the ageing kidney, renal blood flow decreases and the number of functional glomeruli/nephrons decreases without the development of renal failure. On the other hand, age-related deterioration in autoregulation and increased renal vasoconstriction also support this process. In the present study, it was thought that the high resistive index value detected in this study may be related to renal aging and the mentioned mechanisms, although renal failure did not develop. On the other hand, muscle mass loss in geriatric animals may be another reason why creatinine was determined in the reference range but at a lower value and no correlation was detected between the other two parameters. It was evaluated in this study that possible age-related loss of glomeruli/nephrons was probably not at a level to cause an increase in cystatin C and symmetric dimethylargin. These two conditions may explain the high positive correlation between cystatin C and symmetric dimethylarginine, although no significant correlation was found between creatinine and other parameters. The present study provided important data in terms of the parameters evaluated comparatively. Our data emphasise that cystatin C, symmetric dimethylargin and resistive index parameters, which are used as important renal biomarkers in human medicine, can probably be used in the field of veterinary medicine, especially in the evaluation of renal function in geriatric dogs. However, further studies with an increased number of materials, based on a specific age range, breed and sex may provide a clearer understanding of the mechanisms involved.