I’ve been reading some conflicting information on total testosterone and free testosterone.
According to William’s Textbook of Endocrinology 12th ed., bound testosterone is composed of SHBG-bound and Albumin-bound. The text book states that bound T is about 30 - 44% SHBG and 54 - 68% albumin. It also goes on to say that albumin-bound is “bio-available” and useful to the system.
That statement would mean that FT is only part of the equation and that we’d need to monitor the albumin-bound to really track our true testosterone. That idea seems to be contrary to what I’ve read in the stickies.
Things, however, get a little more confusing when you go to Labcorp’s website. I was on there reading about blood test and they have the following statement, "the majority (approximately 60% to 90%) of serum total testosterone is associated with sex hormone binding globin (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". Labcorp and William’s disagree by quite a bit on the amount of T bound to SHBG. They agree, roughly, on the amount of FT as a percentage.
Any insights into these discrepancies? Does albumin-bound T make up a small portion of bound-T?
Link to Labcorp’s test: https://www.labcorp.com/wps/portal/!ut/p/c1/04_SB8K8xLLM9MSSzPy8xBz9CP0os_hACzO_QCM_IwMLXyM3AyNjMycDU2dXQwN3M6B8JG55AwMCuv088nNT9SP1o8zjQ11Ngg09LY0N_N2DjQw8g439TfyM_MzMLAz0Q_QjnYCKIvEqKsiNKDfUDVQEAOrk-dE!/dl2/d1/L0lJWmltbUEhL3dQRUJGUUFoTlFBaERhQUVBWEtHL1lJNXlsdyEhLzdfVUU0UzFJOTMwT0dTMjBJUzNPNE4yTjY2ODAvdmlld1Rlc3Q!/?testId=6305022#7_UE4S1I930OGS20IS3O4N2N6680
Link to William’s Textbook: https://www.amazon.com/Williams-Textbook-Endocrinology-Shlomo-Melmed/dp/1437703240/ref=sr_1_3?s=books&ie=UTF8&qid=1485794226&sr=1-3&keywords=williams+textbook+of+endocrinology