Men, Is Your Testosterone Bioavailable?

Bioavailable testosterone (BT) is either circulating freely or is loosely bound to the blood protein albumin, but is not bound to sex hormone binding globulin (SHBG). BT represents the amount of testosterone readily available for cellular use. 

Evaluating BT can be important clinically even if total testosterone is normal. A decrease in bioavailable testosterone has been associated with high blood pressure, prostate cancer, impaired cognition and memory, and autoimmune disorders, including rheumatoid arthritis.

The relationship between BT and metabolic health is more complex, however. As long as total testosterone and SHBG are optimal, a higher BT is associated with better insulin sensitivity and decreased risk of metabolic syndrome. However, a higher BT, lower total testosterone, and lower SHBG were seen in obese men who were also infertile.

Elevations in BT may reflect overproduction or over-supplementation with testosterone or a low sex hormone binding globulin.

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