Summary:

Testosterone measurement is helpful in evaluation of male and female reproductive issues.

Key Facts:

In males, increased testosterone levels can be found in complete androgen resistance, testicular tumor or precocious puberty; and decreased levels in primary or secondary testicular failure including panhypopituitarism or Klinefelter’s syndrome, and others.

When testosterone levels are slightly elevated in females, hirsutism can develop.  An elevated testosterone in females may be consistent with polycystic ovarian syndrome or masculinizing ovarian tumors. Abnormal production of the androgen in women, to levels similar to those seen in men, can cause virilization.

Once secreted, testosterone is almost entirely bound to transport proteins. In both males and females, testosterone is present in the peripheral circulation in three forms: 

·         Free, unbound (corresponding to the free molecular form)

·         Weakly bound to albumin and to cortisol-binding globulin

·         Tightly bound to sex hormone-binding globulin (SHBG)

The free testosterone is biologically active, and the testosterone weakly bound to albumin can be rendered immediately active through its rapid dissociation from albumin. Therefore, the pool of free and weakly-bound testosterone is collectively called the "bioavailable" or "non-SHBG-bound" testosterone (NSB-T). Estimates of the amount of testosterone in each form are indicated below:

Total testosterone levels may change in concert with the SHBG levels to maintain a constant concentration of free testosterone. It is also expected that when the concentration of free testosterone increases, the total testosterone level will increase and the SHBG level will decrease. The SHBG level is significant because a decreased SHBG level in the presence of a normal or slightly elevated total testosterone level results in more bioactive testosterone, with higher peripheral androgen activity.

Testing Available:

1044:    Total Testosterone

1172:    Free Testosterone

2432:    Total, Free and % Free Testosterone

5965:      Total, Free and % Free Testosterone with Sex Hormone Binding Globulin

References

Smith SW. Free Testosterone. AACC Endo 1993; 11(3):59-62.

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