Luteinizing Hormone (LH)

LH is a pituitary hormone that pulses to the gonads — in women it triggers monthly ovulation and drives ovarian progesterone in the luteal phase; in men it stimulates Leydig cells to make testosterone. LH is interpreted together with FSH and the gonadal-output hormone (testosterone or estradiol) so the clinician can localise the problem. The pattern HIGH LH + low gonadal hormone = primary gonadal failure (ovary or testis isn't responding); LOW LH + low gonadal hormone = pituitary or hypothalamic failure. In women, timing within the menstrual cycle matters: LH surges mid-cycle (the basis of ovulation predictor kits), so a single value is interpretable only with cycle context.

• Menopause / premature ovarian insufficiency — high LH + high FSH + low estradiol.
• Polycystic ovary syndrome (PCOS) — LH:FSH ratio often >2:1.
• Primary testicular failure — Klinefelter's, post-mumps, post-chemotherapy.
• Mid-cycle ovulatory surge — physiological, normal in fertile women.
• GnRH agonist therapy (paradoxical early phase) — therapeutic.

• Hypogonadotropic hypogonadism — pituitary tumour, head trauma, congenital (Kallmann syndrome).
• Hyperprolactinaemia — high prolactin suppresses LH.
• Anorexia nervosa, athletic amenorrhoea — hypothalamic suppression from energy deficit.
• Chronic illness, severe stress — hypothalamic suppression.
• Oral contraceptives, anabolic steroids — exogenous feedback suppression.