Bioavailable testosterone
What it measures, and what changes the number.
Bioavailable testosterone is the part of testosterone in the blood that is not tightly bound to sex hormone binding globulin (SHBG). It includes the free hormone plus the testosterone loosely attached to albumin, which is considered readily available to tissues.
It is read alongside total testosterone, SHBG and albumin, because these determine how testosterone is split between its bound and unbound forms. Free testosterone and LH are often on the same report.
It can be measured directly, commonly by a precipitation method, or calculated from total testosterone, SHBG and albumin, and the two approaches do not always agree. Testosterone varies over the day, so samples are usually taken in the morning, and results are best compared when drawn at a similar time. Labs may print it as Testosterona biodisponible.
Often read alongside: Total testosterone, SHBG, Albumin, Free testosterone (calculated), LH