Elevated serum cystatin C due to acute kidney injury can be reduced to normal with treatment in most cases, while elevated serum cystatin C due to chronic renal insufficiency usually cannot be reduced to normal. Serum cystatin C is an indicator to reflect the glomerular filtration rate of renal function. Since it is not affected by diet and exercise, it can be used to detect impaired renal function at an early stage. 1. If the cystatin C is elevated due to acute renal injury, most of the renal function can be completely restored to normal after treatment of the primary pathology, and the cystatin C can also be restored to normal at this time. 2. In case of chronic renal insufficiency, especially for those who have already had creatinine elevation, due to the decrease in glomerular filtration rate, the cystatin C can not be completely normalized, and it may even lead to the persistent elevation of cystatin C if it is not actively treated.