Direct radioimmunoassay of free testosterone in the evaluation of androgenetic manifestations in women.

The determination or calculation of the non-protein bound fraction of testosterone in serum had been suggested to be superior to the measurement of total testosterone levels in the evaluation of women with clinical signs of hyperandrogenism. We therefore compared the serum concentrations of free testosterone, as determined directly by radioimmunoassay, with the levels of various serum parameters in 317 women with hirsutism or acne. Total testosterone was elevated in 33%, free testosterone in 59%, and DHEA-S in 65% of the patients. Among the women with high levels of free testosterone, 24% showed serum concentrations both of total testosterone and SHBG within the normal range, indicating that the calculation of the testosterone:SHBG ratio (free androgen index) would be of limited value for androgen diagnostics. Serum free testosterone correlated positively with total testosterone and negatively with SHBG. No significant correlation was found between DHEA-S and free or total testosterone, and between total testosterone and SHBG. The stimulation of the adrenal cortex by ACTH resulted only in a significant rise in 17 alpha-hydroxyprogesterone levels. During the dexamethasone suppression test there was a significant suppression of the serum concentrations of total and free testosterone, DHEA-S, and 17 alpha-hydroxyprogesterone, while SHBG did not change. In several of the women with normal testosterone levels, free testosterone decreased by more than 50%, although the suppression of total testosterone was only slight. This was possibly due to the suppression of adrenal androgens which may compete with testosterone for the binding sites of SHBG. The direct measurement of free testosterone appears to be a valuable approach to the evaluation of women with androgenetic manifestations.