Serum cystatin C is a relatively important index in renal function tests, and has been widely used in clinical practice in recent years. Serum cystatin C can reflect abnormal renal function more accurately and sensitively because the kidney is the only organ that clears serum cystatin C. It is generally not affected by tumors, inflammation, etc. It can be freely filtered through the kidney, mainly by the glomerulus in the proximal tubule is reabsorbed and degraded, not excreted by the renal tubules, and it can reflect the endogenous creatinine clearance more accurately. Compared with creatinine, which is generally elevated only at 1/2 of the decline in renal function and is relatively slow to respond, serum cystatin C can reflect changes in renal function more quickly and sensitively than creatinine. Its clinical significance is that if serum cystatin C is elevated it indicates glomerular filtration dysfunction and renal damage, and if renal tubular reabsorption dysfunction is present, a significant increase in urinary cystatin C can be found. If the serum cystatin C is lower than the normal value, it is generally not clinically significant.