This kit is used for quantitative determination of retinol binding protein (RBP) in human serum, plasma or whole blood in vitro. Retinol binding protein is a protein involved in vitamin a transport in the blood, which is synthesized by the liver and widely distributed in the blood, cerebrospinal fluid, urine and other body fluids. The determination of retinol binding protein can detect the functional damage of renal tubules in the early stage and sensitively reflect the damage degree of renal proximal convoluted tubules; it can also be used as an indicator of early damage of liver function and monitoring treatment; it can also more sensitively reflect the nutritional status of the body, especially the change of protein metabolism in a short period of time, and can detect early and subclinical malnutrition.