Cystatin C: a kidney function biomarker.

Renal function is essential for homeostasis. The kidneys play important pleiotropic roles including removal of metabolic waste products and maintenance of water-electrolyte balance and blood pressure. Early diagnosis of renal dysfunction and institution of appropriate therapy are vital to survival. Unfortunately, common indicators of renal function lack necessary sensitivity and specificity. Recent evidence has, however, suggested that cystatin C (cysC) may be useful as a marker for glomerular filtration. CysC is a protein belonging to a group of cysteine proteases inhibitors produced primarily by nucleated cells. Due to low molecular weight and positive pI, it is easily filtered. Moreover, its serum concentration is independent of gender, age, or muscle mass, i.e., typical confounders in assessing glomerular filtration rate (GFR). This chapter discusses the structure and biologic function of cysC, its role as an indicator of GFR, and the most frequently used methods for its determination.