Cystatin C a protein encoded by the CST3 gene, with molecular weight of 13260 Da, is composed of 120 amino acids, lacks carbohydrate and has two disulfide bridges located near the carboxyl terminus. Cystatin C is mainly used as a biomarker of kidney function. If kidney function and glomerular filtration rate decline, the blood levels of cystatin C rise. Recently, it has been studied for its role in predicting new-onset or deteriorating cardiovascular disease. It also seems to play a role in brain disorders involving amyloid (a specific type of protein deposition), such as Alzheimer's disease.