The HPG Axis — Why Multiplex Measurement Matters

The hypothalamic-pituitary-gonadal (HPG) axis is a closed-loop feedback system: GnRH from the hypothalamus stimulates pituitary FSH and LH release, which drive ovarian follicular development and steroidogenesis (Estradiol, Progesterone) or testicular testosterone production. Measuring a single hormone at a single timepoint provides a snapshot — but reproductive endocrinology requires understanding the dynamic relationships between pituitary drive, gonadal output, and regulatory proteins. Multiplex measurement captures the integrated HPG axis profile that reveals the feedback state — whether the ovary is responding appropriately to gonadotropin stimulation, whether elevated LH relative to FSH suggests PCOS, or whether elevated FSH with low estradiol indicates menopause.

Reproductive Hormone Markers

  • Pituitary Gonadotropins: FSH drives follicular recruitment and granulosa cell proliferation. LH triggers ovulation and luteinization; the LH:FSH ratio is elevated in PCOS. Both are pulsatile — single measurements reflect the integrated signal.
  • Gonadal Steroids: Estradiol (E2) is the primary ovarian estrogen, feeding back to suppress FSH. Progesterone confirms ovulation. Testosterone is elevated in PCOS and congenital adrenal hyperplasia.
  • Regulatory & Binding Proteins: SHBG regulates free steroid availability and is decreased in PCOS. Prolactin suppresses GnRH when elevated. hCG is a placental gonadotropin. AMH is the leading marker of ovarian reserve.