Sex hormone-binding globulin (SHBG) and albumin are two examples of proteins that are not bound to testosterone in the bloodstream, which is referred to as free testosterone. In contrast to total testosterone, which is made up of both bound and free testosterone, free testosterone is easily absorbed by body cells.

A important hormone, testosterone is mostly produced in the testes of males and in smaller amounts in the ovaries of females. It is essential to several physiological functions, such as:

development and upkeep of the testes and prostate gland, two male reproductive organs.
enhancement of secondary sexual traits in men, such as the increase of muscle mass, the growth of facial and body hair, and a deeper voice.
Control of libido (sex desire) and sexual processes in men