Determination of testosterone in serum not bound by sex-hormone-binding globulin: diagnostic value in hirsute women.

We compared the diagnostic value of information given by total testosterone (I), free testosterone (II), the free androgen index (III), and testosterone not bound by sex-hormone-binding globulin (SHBG) (IV) as measured by a new differential ammonium sulfate precipitation technique, each step of which is conducted at 37 degrees C. SHBG and albuminemia were also measured. To examine the clinical value of IV, we analyzed single blood samples from 15 hirsute women and 15 age-matched healthy control volunteers. Values for I, II, III, and IV testosterone were all significantly higher in the hirsute group (P less than 0.01), whereas SHBG was decreased (P less than 0.01) and albumin concentrations were similar for the two groups. Overlap between values for normal and for hirsute women was 33.3% for I, 13.3% for II, and 0% for III and IV. The presented data suggest that IV measured by ammonium sulfate precipitation is the preferred discriminator for detecting hyperandrogenism, because this assay is technically simpler and less expensive than the II assay for routine investigation. It closely reflects the pool of bioavailable testosterone; thus, its main use might be as a screening test for androgen excess in women.