Luteinizing hormone (LH) is a hormone produced by gonadotropic cells in the anterior pituitary gland. It is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. LH plays an important role in sexual development and functioning. In females, an acute rise of LH known as an LH surge triggers ovulation and development of the corpus luteum. In males, LH stimulates Leydig cell production of testosterone and acts synergistically with follicle-stimulating hormone (FSH) . LH is a heterodimeric glycoprotein, and each monomeric unit is a glycoprotein molecule; one alpha and one beta subunit make the full, functional protein. LH is part of a complex communication network that involves the hypothalamus, pituitary gland, and sex organs.

A luteinizing hormone test measures how much LH is in the blood. LH levels can be used to diagnose pituitary gland problems and infertility. Normal LH numbers depend on sex and age, and LH levels fluctuate throughout development. In women, normal results are 5-25 international units per liter (IU/L) before menopause and 14.2-52.3 IU/L after menopause. In men, LH is released at a constant pace over time, and testosterone is produced at a constant level.