Cysteine protease inhibitor C belongs to the cysteine protease inhibitor superfamily and is an effective inhibitor of lysosomal proteases, possibly one of the most important extracellular inhibitors of cysteine proteases. It exists in almost all tissues and bodily fluids, including plasma, urine, and cerebrospinal fluid. Cystatin C participates in various disease processes by regulating cysteine protease activity. Cystatin C is mainly used as a biomarker for renal function. Recently, research has shown that it plays a role in predicting new or worsening cardiovascular diseases. In addition, it plays a role in amyloid related brain diseases such as Alzheimer’s disease.