High serum cystatin C may indicate impaired glomerular filtration function and requires active diagnosis and treatment. Serum cystatin C is a protein that can freely pass through the glomerular filtration membrane and is secreted in a relatively constant amount. It is basically absorbed and broken down by the epithelial cells in the proximal tubules of the kidneys, and therefore does not return to the blood. The normal reference value of cystatin C in serum is 0.6~2.5mg/L, when its value is elevated, it suggests that the glomerular filtration function may be abnormal. Compared with blood creatinine, urea nitrogen and other tests, it is more sensitive in determining the early damage of renal function, so it can be used to assess the early damage of renal filtration function in diabetic nephropathy, and to detect the renal damage of chemotherapeutic drugs, etc. However, it is not the case that Cystatin C is high. However, high cystatin C does not mean abnormal renal function, it needs to be combined with other tests such as urine test and renal ultrasound to further evaluate the condition. It is recommended to consult a doctor in time for standardized diagnosis and treatment.