Serum cystatin is a small molecular weight protein that can be filtered out by the glomerulus and is not secreted by the renal tubular epithelium and is not reabsorbed, so it can reflect the filtration function of the glomerulus. If the serum cystatin is increased, it indicates some damage of kidney function. Combine with blood creatinine, blood urea nitrogen, uric acid, urinary ultrasound and other indicators to further clarify whether there is impaired renal function. If the renal function is indeed impaired, the primary cause of renal insufficiency needs to be clarified, and then active clinical treatment should be given for the cause, and we should not wait blindly to prevent delaying the disease.