Cystatin C has been a simple, accurate, and rapid endogenous biomarker of glomerular filtration rate (GFR) in research and clinical practice for testing kidney function. Its role has been studied in predicting newonset or deteriorating cardiovascular diseasea cysteine proteinase inhibitor that is involved in kidney function, cardiovascular disease and neurologic disorders. It has been shown to colocalize with amyloid beta in brain disorders such as Alzheimer disease. Cystatin C is expressed in human 293 cells as a monomer with a molecular mass of 12 to 13 kDa.