Test Details: IGF BP3 is the main carrier of somatomedin C in the body. Blood level of both of these proteins are controlled by human growth hormone that is produced by the pituitary gland. IGFBP 3 is more than just a transporter. It also helps extend the life of somatomedin C in the blood. Levels are highest during chilhood and puberty but decrease during adulthood. Done to indicate whether someone is producing normal amount of growth hormone.