Obesity regulates bioavailable testosterone levels in women with or without polycystic ovary syndrome

Abstract

Objective: To evaluate [1] the effects of levels of sex hormone-binding globulin (SHBG), albumin, and total testosterone on the distribution of testosterone between SHBG-bound and non–SHBG-bound fractions; [2] the independent effects of polycystic ovary syndrome (PCOS) and body mass index on serum levels of total testosterone, non–SHBG-bound testosterone, SHBG, and albumin; and [3] the usefulness of levels of total testosterone and non–SHBG-bound testosterone and of the free androgen index in the diagnosis of PCOS. Design: Retrospective clinical study. Setting: An academic research environment. Patient(s): Forty-three women with oligomenorrhea and PCOS. Twenty-five women with regular menstrual cycles and without hirsutism served as controls. Intervention(s): None. Main Outcome Measure(s): Levels of non–SHBG-bound testosterone, total testosterone, SHBG, and albumin in serum. Result(s): Levels of total testosterone and non–SHBG-bound testosterone, and the free androgen index were higher in patients with PCOS than in healthy controls. PCOS did not have an effect on the levels of SHBG or albumin, or on the percentage of non–SHBG-bound testosterone. Levels of SHBG and albumin were inversely related to body mass index. The percentage and concentration of non–SHBG-bound testosterone and the free androgen index were directly related to body mass index. Hirsutism did not have an effect on any outcome measure. Conclusion(s): The distribution of total testosterone into SHBG-bound and non–SHBG-bound fractions is associated with body mass index, not with PCOS. The high levels of non–SHBG-bound testosterone and the high free androgen index in patients with PCOS reflect mainly high levels of total testosterone. Thus, the measurement of levels of non–SHBG-bound testosterone and the calculation of the free androgen index provide no further information in the diagnosis of PCOS beyond that provided by the measurement of levels of total testosterone.