Prealbumin, formally known as Transthyretin, is a hormone produced by the liver. Secreted into the bloodstream, Prealbumin carries thyroxine and is responsible for regulating metabolism, which is the use of energy in the body. The test is recommended by doctors mainly to assess malnutrition and the level of proteins in the bloodstream. The test is usually assigned to a patient who has undergone trauma, lost a lot of weight, or suffers from a chronic illness.