LH (Luteinizing Hormone): Physiology, Testing, and Clinical Interpretation

Luteinizing Hormone (LH) is a gonadotropin secreted by the anterior pituitary gonadotrophs. Its pulsatile release, driven by GnRH, regulates gonadal function in both sexes.

Physiology

• Women: Mid-cycle LH surge triggers ovulation; supports corpus luteum progesterone production. Pulsatile in follicular phase.
• Men: Stimulates Leydig cells to produce testosterone. Pulsatile, GnRH-driven.

Clinical Testing Indications

• Infertility workup: Day 3 FSH/LH ratio; PCOS often shows LH:FSH >2–3:1.
• Ovulation prediction: Urine LH surge kits detect the preovulatory surge.
• Hypogonadism differential: Low LH + low sex steroids = central (hypogonadotropic); High LH + low sex steroids = primary (hypergonadotropic).
• Puberty disorders: Basal/stimulated LH assesses precocious or delayed puberty.
• Menopause confirmation: Elevated LH/FSH confirms ovarian failure.

Assay & Interpretation

Measured by sandwich immunoassay (chemiluminescence). Reference ranges are assay-dependent; always interpret in clinical context with concurrent FSH, estradiol/testosterone, and clinical picture.