Reference intervals for serum sex steroids and gonadotropins in regularly menstruating women

Reference intervals for novel fluoro-immunoassays for serum luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E(2)) and progesterone (P) were established in 40 healthy regularly menstruating women. Serum samples for sex steroids, including testosterone (T), androstenedione (A) and dehydroepiandrosterone sulphate (DHEAS), as well as sex hormone binding globulin (SHBG) and gonadotropins, were collected in the early follicular and mid-luteal phases of the menstrual cycle. The need for the timing of androgen and gonadotropin samples was also determinated. Serum E(2) and P were measured by radio-immuno- and time-resolved fluoro-immunoassays. Various assay methods correlated closely, but the reference intervals varied considerably from one method to another. In the early follicular phase the LH/FSH ratio only ranged between 0.2 and 1.7 (mean +/- S.D.; 0.8 +/- 0.3); the variation was greater (from 0.3 to 3.5) in the luteal phase, when the mean was also significantly higher (1.5 +/- 0.9, p = 0.0001). Similarly the mean values of T and SHBG were higher in the luteal phase, while the other androgen concentrations and calculated androgen indexes were equal, compared with the follicular phase values. Thus the timing of hormone determinations is warranted in the investigation of the gonadotropin and androgen status in normally menstruating women. Moreover, the upper limit of the LH/FSH ratio examined with new, sensitive methods is lower than that previously stated. The use of an intra-uterine contraceptive device (IUD) had no effect on hormone levels.