The fraction of testosterone not tightly bound to SHBG and therefore available to tissues.
Also known as: free and albumin-bound testosterone
Most testosterone in blood is bound to sex hormone binding globulin (SHBG) or albumin. Bioavailable testosterone refers to the portion that is free or loosely albumin-bound and can act on tissues.
Because SHBG levels change the amount of active hormone, clinicians sometimes look at bioavailable or free testosterone rather than total testosterone alone.