Free testosterone concentration in serum: elevation is the hallmark of hirsutism.

A simple, reliable procedure for quantitating the concentration of free (not protein bound and thus biologically active) testosterone in serum has been applied to normal and hirsute patients. Each of 32 hirsute women studied had a significantly elevated level of free testosterone (that is, more than two standard deviations above the mean of that found in normal women), although half of them had a total serum testosterone level within normal limits. Suppression of free testosterone to within normal limits could be accomplished by dexamethasone alone in 47 per cent of the hirsute group. In the remainder of the hirsute group, suppression of free testosterone to within normal limits could be accomplished by addition of Enovid-E. Use of free serum testosterone concentration is clearly superior to the use of total serum testosterone concentration for the identification and rational therapy of simple hirsutism.