There is no such thing as how much high serum cystatin C is considered serious. Serum cystatin C greater than 2.5 mg/L should be alerted to the presence of impaired renal function, and is a specific indicator for evaluating glomerular filtration function. Cystatin C, i.e. cysteine protein inhibitory protein C, is secreted in a relatively constant amount every day, so it can sensitively reflect mild renal injury. However, serum cystatin C is generally not able to evaluate the severity of renal function, and creatinine and creatinine clearance are commonly used to evaluate the severity of renal function in clinical practice. Serum cystatin C can reflect the situation of kidney injury earlier than urea nitrogen and creatinine, so when cystatin C is abnormal, you must go to the regular hospital and choose the appropriate treatment under the guidance of professional doctors.