NOTE: One interesting fact about erythropoitin is that it is also called EPO, a name that may be more familiar to some of you. Yes, that should bring the name Lance Armstrong to mind. Lance Armstrong confessed to using EPO as a performance enhancing drug strictly for the purpose of raising his red blood cell counts for racing purposes. Basically, he was doing a different and very dangerous kind of steroid. Giving EPO to these racers leaves them vulnerable to dieing in their sleep from the "sludging" of the blood that occurs. It does turn them into superhumans however.
It is suggested that bioavailable testosterone 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 bioavailable testosterone. Decreased SHBG levels can be seen in obesity, hypothyroidism , androgen use, and nephritic syndrome (a form of kidney disease ). Increased levels are seen in cirrhosis , hyperthyroidism , and estrogen use. In these situations, measurement of free testosterone may be more useful.