Luteinizing hormone (LH) is synthesized by the pituitary gland, a small gland at the base of the brain.
LH is associated with ovulation in women and testosterone production in men. In adults, LH testing is indicated in cases of infertility and menstrual cycle disorders. In men, the test is indicated in cases of infertility or low testosterone levels (hypogonadism).
The secretion of LH in women is cyclical, with an increase at the beginning of the cycle, a significant peak mid-cycle coinciding with ovulation followed by progesterone production, and an end-of-cycle decrease that triggers menstruation. LH levels must be interpreted in light of FSH, estradiol, progesterone or testosterone levels. In menopausal women, LH secretion is increased by the pituitary gland in an attempt to restimulate estradiol production by non-functional ovaries.
High levels of LH in an infertile or hypogonadic individual indicate an impairment of the sex organs (ovaries, testicles) rather than a problem with the pituitary gland. Low levels of LH will instead direct the investigation to a pituitary condition. A high result in perimenopausal women helps confirm the onset of menopause.