Testosterone, free testosterone, and free androgen index in women: Reference intervals, biological variation, and diagnostic value in polycystic ovary syndrome

The objective of our study was to determine reference intervals and biologic variation for testosterone (T), free testosterone (fT), and free androgen index (FAI) in women with accurate methods and to test the discriminative value of these parameters in a polycystic ovary syndrome (PCOS)-population. Serum was obtained daily during a normal menstrual cycle from 25 healthy women (677 data-points). A single serum sample was obtained from 44 PCOS-patients. T was measured by LC–MS/MS and by Architect® 2nd generation T Immunoassay. Sex hormone-binding globulin was measured to calculate fT and FAI. Reference intervals which were established in healthy women with an ovulatory menstrual cycle were T=0.3–1.6nmol/L and 0.5–2.0nmol/L, fT=5.2–26pmol/L and 7.2–33pmol/L, and FAI=0.4–2.9 and 0.6–4.4, by LC–MS/MS and immunoassay, respectively. T, fT and FAI were higher in PCOS patients than in controls (p