Determination of the glomerular filtration rate (GFR) is a valuable parameter for estimating kidney function and staging renal disease. The simplest and most accurate method for determining GFR in clinical practice is the measurement of plasma clearance using iohexol. However, this technique is technically demanding and costly. Therefore, GFR is commonly assessed indirectly through renal biomarkers.

Renal diseases are frequently diagnosed in geriatric cats and dogs. Among the parameters used to evaluate renal function, serum creatinine is the most widely employed indirect biomarker. Although serum creatinine exhibits high specificity for kidney damage, its sensitivity is reduced at values close to the upper reference limit. It is generally accepted that at least 75% of the nephron mass must be lost before serum creatinine levels exceed the upper reference range.

In geriatric cats and dogs, age-related decreases in muscle mass are observed. Due to this relative reduction in muscle mass, serum creatinine levels in these animals tend to be lower than normal, which may misleadingly suggest better renal function than is actually present. Cystatin C and symmetric dimethylarginine (SDMA) have been reported as potential endogenous markers of glomerular filtration rate. These biomarkers are useful and promising for detecting and monitoring declining renal function.

Renal diseases are commonly diagnosed in geriatric cats and dogs, with a high prevalence of chronic kidney disease in this population. Research aimed at identifying new biomarkers that could facilitate the early diagnosis of renal disorders is increasing steadily.