The normal value of cystatin C ranges from 0.6 to 2.5mg/L, with slight variations in different laboratories. It is a sensitive indicator of the kidney, and its abnormal value can be seen in physiological conditions such as strenuous exercise, as well as in pathological conditions such as acute or chronic damage to the kidneys. Cystatin C, also known as serum cystatin C, is a cysteine protease inhibitor, produced by the nucleus of human nucleated cells, which can be removed by glomerular filtration, and therefore can stably reflect the glomerular filtration function. Normally, cystatin C above 2.5mg/L indicates an abnormal cystatin C test. After strenuous exercise, due to the accelerated glomerular filtration rate of the kidneys, there can be a physiological decrease in cystatin C value without any clinical significance, while glomerular diseases, chronic diabetic nephropathy, and other pathological conditions can cause a pathologic increase in cystatin C. It is recommended that people with abnormally elevated cystatin C results should consult a doctor in a timely manner to clarify the cause of the disease and standardize the treatment under the doctor’s guidance.