Free vs. Bioavailable T

[tm123]

Hi guys. My Dr. said that "bioavailable" testosterone level is really the one that is most important to measure. Most of all the posts I see here make a distinction between total and free, but not bioavailable. Another doctor I went to didn't even test bioavailable, only total and free. Can someone explain this discrepancy? I've tried searching for the answer but have not had much luck. Thanks very much.

[lovbyts]

The term bioavailable testosterone (BAT) refers to the sum of free testosterone plus albumin-bound testosterone.

What are free and bioavailable testosterone?
Testosterone is present in the blood as "free" testosterone (1-4%) or bound testosterone. The latter may be loosely bound to albumin, a serum protein, or bound to a specific binding protein called Sex Steroid Binding Globulin (SSBG) or Sex Hormone Binding Globulin (SHBG). The binding between testosterone and albumin is not very strong and is easily reversed; so the term bioavailable testosterone (BAT) refers to the sum of free testosterone plus albumin-bound testosterone. Alternatively, it is the fraction of circulating testosterone that is not bound to SHBG. It is suggested that BAT represents the fraction of circulating testosterone that readily enters cells and better reflects the bioactivity of testosterone than does the simple measurement of serum total testosterone. Also, varying levels of SHBG can result in inaccurate measurements of BAT. Decreased SHBG levels can be seen in obesity, hypothyroidism, androgen use, and nephritic syndrome. Increased levels are seen in cirrhosis, hyperthyroidism, and estrogen use. In these situations, measurement of free testosterone may be more useful. However, technically, free testosterone is difficult to measure accurately.

[Dancer]

/\ good post