Retinol Binding Protein is a protein synthesized by the liver that binds vitamins in the body, aids in vitamin transport, and is widely found in blood, cerebrospinal fluid, and other body fluids. We measure retinol-binding protein as a response to liver and kidney function and some disease states can alter the level of this protein. A low retinol binding protein can indicate a serious infection, and liver diseases such as cirrhosis, liver failure, and hyperthyroidism can cause a decrease in retinol binding protein.