Use

Free testosterone is the concentration of unbound testosterone in serum.1 The majority (approximately 60% to 90%) of serum total testosterone is associated with sex hormone binding globulin (SHBG); this fraction is tightly bound and biologically unavailable to its target tissues. The remaining bioavailable testosterone is mostly bound to albumin, with only a small fraction (approximately 0.5% to 2%) circulating in the free form.1,2 Free testosterone is the form of testosterone that can diffuse into the tissues and act on receptors and is considered the active fraction by many physicians.1,3,4 Free testosterone assessment is recommended as a primary or secondary measure of androgen activity in men2,5-11 and women.12-16 The equilibrium dialysis or ultrafiltration methods are recommended, however they are relatively difficult and expensive to perform. All of these methods are currently available from LabCorp.