Description:

Free testosterone – molecules of the male hormone that circulate freely in the blood and are not bound to proteins, such as SHBG. Testosterone is almost entirely bound to transport proteins. Thus, in both males and females, testosterone is present in the peripheral circulation in three forms: - free, unbound (corresponding to the free molecular form); - weakly bound to albumin and to cortisol-binding globulin; and - tightly bound to sex hormone-binding globulin (SHBG). The free testosterone is biologically active, and the testosterone weakly bound to albumin can be rendered immediately active through its rapid dissociation from albumin. Therefore, the pool of free and weakly-bound testosterone is collectively called he\"bioavailable\" or SHBG-bound\" testosterone (NSB-T) Based on a DPC study on 81 females ovulating, on oral contraceptives, and postmenopausal; and on 87 males, aged 20 to over 50 years. A somewhat different range of values for free testosterone as a percent of total testosterone is obtained with various methodologies used to estimate the proportions of the three testosterone pools (free, weakly bound, tightly bound).