Cystatin C clinically refers to serum cystatin C, a protein that inhibits the catabolism of other proteins, and the measured value is primarily used in the evaluation of renal function. Low cystatin C generally suggests that kidney filtration is good, and may also be seen in conditions such as early diabetic nephropathy where glomerular filtration rate is elevated. Serum cystatin C is produced by most cells in the body and is almost completely broken down in the kidneys; if the kidneys are not working properly, cystatin C can build up in the blood. The cystatin C test is not affected by inflammation, tumors, liver function, or other factors, and it can detect kidney damage more quickly. If Cystatin C is high, it generally indicates that the glomerular filtration function is reduced, which suggests poor kidney function, and its detection value is related to the degree of renal impairment, which needs to be improved by other related tests for comprehensive judgment. Low cystatin C generally does not have much clinical significance, it is recommended to improve the relevant examinations in a timely manner, combined with clinical symptoms for comprehensive analysis.