Cystatin-C (CYSC) is a non-glycosylated, low molecular weight, cation protein that is regularly synthesized by most nucleated cells. Cystatin-C is an endogenous protein that is known to be affected little by age, race, and muscle mass. It is not only used as a biomarker of renal function but also has positive associations with obesity, insulin resistance, hypertension, and cardiovascular mortality. Higher levels of serum cystatin-C were associated with increased prevalence of diabetic conditions.

Under normal circumstances, cystatin C in serum is 0.47-1.09 mg/L. When renal function is impaired, cystatin C concentration in blood will change with GFR. In renal failure, GFR decrease while cystain C concentration in blood can increase more than 10 times. Under normal glomerular filtration rate and renal tubules dysfunction can hinder cystatin C absorption and its rapid decomposition in the renal tubules, increasing its concentration in urine over 100 times.