The four indicators of early kidney damage should refer to the markers of early kidney injury. Currently, the commonly used markers of early injury are retinol binding protein, α1-microglobulin, β2-microglobulin, N-acetyl -β-D-glucosidase and four of urinary microalbumin. Early markers are needed to determine whether a patient has kidney damage, as there are usually no clinical manifestations in the early stages of kidney disease. The glomerulus has two barriers, the filtration barrier and the charge barrier. Normally, the size of albumin is just not able to pass the filtration barrier, but when very small lesions occur in the glomerulus, trace amounts of albumin can be detected in the urine, so this item will be detected. The proximal tubule is the only site of β2-MG processing in the body, so when minor lesions occur in the proximal tubule, the amount of urinary β2-MG increases significantly. It is generally accepted that measurement of α1-MG in serum and urine is a sensitive indicator of impaired renal tubular reabsorption and is somewhat superior to β2-microglobulin. Urinary NAG activity reflects the lesion of renal parenchyma, especially sensitive to acute injury and active stage, and can be used for early detection of renal injury and observation of disease course. The above indicators are often used for clinical judgment.