Changes in SHBG can affect the amount of testosterone that is available to be used by the body. Normally, about 45% of testosterone in men and about 70% in women, is tightly bound to SHBG, and most of the rest is weakly and reversibly bound to another protein, albumin. Only about 1-3% is not bound and immediately available to the tissues as free testosterone.
A total testosterone test does not distinguish between bound and free testosterone; it measures the overall quantity of testosterone. In many cases, this measurement is sufficient to discover excessive or deficient testosterone production; but, if a patient’s SHBG level is not normal, then the total testosterone may be misleading.
