Comparison of serum creatinine cystatin C and blood gas measurement results in geriatric dogs

Changes that occur with ageing also affect the kidneys. Although a gradual decline in renal function is expected in geriatric animals, renal dysfunction does not become apparent on routine assessment before significant nephron loss occurs. With advancing age, renal blood flow decreases, renal ischaemia may develop and glomerular filtration rate decreases as a result. For all these reasons, renal failure is more common in geriatric animals. However, creatinine is mainly affected by dehydration and loss of muscle mass. Due to these limitations, it may not be possible to detect the decrease in glomerular filtration rate early in the routine control of geriatric animals and may cause delay in diagnosis. On the other hand, cystatin C is reported to be more useful in the evaluation of glomerular filtration rate. The aim of this thesis was to determine the relationship between serum creatinine, cystatin C and venous blood gas measurements in geriatric dogs. The animal material of the study consisted of 50 geriatric dogs which were clinically healthy, free of chronic diseases and aged between 6.5-15 years depending on the breed. Haemogram, biochemistry and blood gases were measured in the blood samples. Although the mean serum creatinine concentration was determined within the reference range in geriatric dogs, an increase in serum cystatin C level was observed in the same group. The mean pH of 7.34 was considered to be slightly low, while other venous blood gas parameters were within the normal range. No correlation was found between serum creatinine and cystatin C and between serum cystatin C and venous blood gas values. However, a moderate to low level negative correlation was found between serum creatinine and pH and bicarbonate parameters. In conclusion, it was concluded that loss of organ function and possible age-related reduction in muscle mass should be taken into consideration in the clinical laboratory evaluation of geriatric patients and cystatin C measurements may be included in routine renal function tests. On the other hand, it is a fact that additional studies on a larger number of geriatric dogs are needed to clearly demonstrate the correlation of this biomarker with serum creatinine and blood gas parameters. The lack of a significant correlation between serum creatinine and cystatin C is an important result of this study.