Cystatin C is a sensitive and specific indicator of glomerular filtration function. Cystatin C, i.e. cysteine protein inhibitory protein C, is produced by the body at a constant level and is not affected by other factors, which makes it more sensitive to evaluate glomerular filtration function. Regular monitoring of cystatin C can dynamically observe the development of renal disease in diabetic nephropathy; it can promptly respond to the recovery of renal function in renal transplantation, and quickly diagnose acute rejection or damage caused by drug therapy. The reference value of adult serum cystatin C is 0.6~2.5mg/L, which is more timely and early response to early kidney injury than blood creatinine and urea nitrogen. Moreover, the dose of drugs can be adjusted according to serum cystatin C during chemotherapy treatment.