Cystatin C, which is cleared only by glomerular filtration, is an endogenous marker reflecting changes in glomerular filtration rate, and it is essential to evaluate the renal function status of patients with DKD and DKD+NDKD with a reliable GFR in the early stages of the disease, and several studies have found that the level of cystatin C is elevated earlier than creatinine (35, 36). This evidence concerns the gene CST3 and diabetic kidney disease.