Low cystatin C is of no practical significance. Cystatin C is also known as a cysteine protease inhibitor. The cystatin C circulating in the body is filtered by the glomerulus, and after filtration it is reabsorbed in the proximal tubule, and after reabsorption it is completely catabolized and cannot be returned to the blood, so cystatin C can be used to evaluate the glomerular filtration rate and is not interfered by any other factors, making it an ideal marker for diagnosing the glomerular filtration rate in clinical practice. If the level of cystatin C is low in the body, the glomerular filtration rate is effective and increased, which is beneficial for the human organism itself. If cystatin C increases and is deposited in the blood, it indicates a decrease in glomerular filtration rate, impaired kidney function, and possible kidney disease.