Luteinizing hormone (LH) is a hormone associated with reproduction and the stimulation of the release of an egg from the ovary (ovulation) in women and testosterone production in men. This test measures the amount of luteinizing hormone in the blood or urine.
LH is produced by the pituitary gland, a grape-sized organ found at the base of the brain. Control of LH production is a complex system involving the hypothalamus in the brain, the pituitary gland, and the hormones produced by the ovaries and testicles.
In premenopausal women, several hormones rise and fall in a specific sequence during each menstrual cycle. During the cycle, LH stimulates ovulation and the production of other hormones, estradiol and progesterone.
Womens’ menstrual cycles are divided into follicular and luteal phases, with each phase lasting about 14 days. Near the end of the follicular phase, there is a mid-cycle surge of follicle-stimulating hormone (FSH) and LH. This surge triggers ovulation, causing the rupture of the egg follicle on the ovary and the release of the egg.
During the luteal phase, the site where the egg follicle ruptured becomes a “corpus luteum.” LH secretion stimulates the corpus luteum to start producing progesterone. FSH and LH levels decline, while progesterone and estradiol concentrations increase. These hormone levels decrease in turn after several days if the egg is not fertilized. Menstruation starts and when it ends, the cycle begins again.
As a woman ages and menopause approaches, ovarian function wanes and eventually ceases. As this occurs, FSH and LH levels rise.
In men, LH stimulates Leydig cells in the testicles to produce testosterone. LH levels are relatively constant in men after puberty. A high testosterone level provides negative feedback to the pituitary gland and the hypothalamus, thus decreasing the amount of LH secreted.