Luteinizing hormone (LH) is a reproductive hormone that triggers ovulation in women and drives testosterone production in men. It’s made by the pituitary gland, a pea-sized structure at the base of your brain, and released into the bloodstream in response to signals from the hypothalamus. Despite its small quantity, LH plays an outsized role in puberty, fertility, and sexual function throughout your life.
How LH Works in Women
LH’s most well-known job in women is triggering ovulation. During the first half of your menstrual cycle, rising levels of follicle-stimulating hormone (FSH) help an egg mature inside the ovary. Then, around the middle of the cycle, the pituitary gland releases a sharp burst of LH called the “LH surge.” This surge sets off a chain reaction: the mature egg resumes its final stage of cell division, the follicle surrounding it breaks open, and the egg is released into the fallopian tube.
After ovulation, LH takes on a second critical role. The ruptured follicle transforms into a temporary gland called the corpus luteum, and LH is the primary hormone keeping it alive and functional. The corpus luteum pumps out progesterone, the hormone that thickens the uterine lining and prepares it for a fertilized egg to implant. If pregnancy occurs, the corpus luteum continues producing progesterone to support the early weeks until the placenta takes over. If pregnancy doesn’t occur, LH support drops, the corpus luteum breaks down, progesterone falls, and your period begins.
How LH Works in Men
In men, LH travels through the bloodstream to the testes, where it locks onto receptors on specialized cells called Leydig cells. This binding activates a cascade inside the cell that ultimately converts cholesterol into testosterone. The process involves cholesterol being shuttled into the cell’s mitochondria, then passed through several conversion steps in different parts of the cell until testosterone is the final product.
Testosterone produced this way is essential for sperm production, muscle development, bone density, sex drive, and the physical changes of puberty. LH also influences how Leydig cells grow, mature, and function over time. Without adequate LH signaling, testosterone levels drop and sperm production can stall or stop entirely.
The Feedback Loop That Controls LH
LH doesn’t operate on its own. It’s part of a tightly regulated communication loop between three structures: the hypothalamus, the pituitary gland, and the gonads (ovaries or testes). The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses, which tells the pituitary to produce and release LH. The sex hormones produced downstream, primarily estrogen and testosterone, circle back to the hypothalamus and pituitary to dial LH production up or down.
When sex hormone levels are adequate, this negative feedback keeps LH in check. When sex hormone levels drop, whether from aging, injury, or disease, the brake comes off and LH levels climb. This is why LH levels rise naturally during menopause: the ovaries produce less estrogen, so the pituitary compensates by releasing more LH.
Normal LH Levels
LH levels vary by sex, age, and where a woman is in her menstrual cycle. For adult women before menopause, the typical range is 5 to 25 IU/L, with a spike well above that baseline during the mid-cycle surge. After menopause, normal levels rise to roughly 7.7 to 58.5 IU/L. For adult men, the range is narrower: 1.8 to 8.6 IU/L. In children, LH levels are normally very low until puberty begins.
What High LH Levels Mean
High LH doesn’t always signal a problem. During the mid-cycle surge, elevated LH is completely normal and simply means ovulation is happening. But consistently high LH levels throughout the month can point to something else.
In women of childbearing age, persistently elevated LH may indicate polycystic ovary syndrome (PCOS), primary ovarian insufficiency, thyroid or adrenal disorders, or a chromosomal condition like Turner syndrome. In women over 45, high LH typically signals the approach of menopause. In men, elevated LH can result from testicular damage, whether from injury, mumps, autoimmune disease, or cancer treatment like chemotherapy or radiation. A type of tumor called a germ cell tumor and chromosomal conditions like Klinefelter syndrome can also push LH levels up. In children, high LH alongside high FSH may indicate precocious puberty, where sexual development begins unusually early.
What Low LH Levels Mean
When LH is too low, the gonads don’t get the signal they need. The result is a condition called hypogonadotropic hypogonadism, which can be present from birth or develop later in life. In men, this means low testosterone, reduced sex drive, weight gain, and infertility. In women, it can cause missed periods and difficulty conceiving.
Congenital forms include Kallmann syndrome, which pairs low LH with an absent or diminished sense of smell, and idiopathic hypogonadotropic hypogonadism, where the cause is genetic but smell is unaffected. Acquired causes are more varied: pituitary tumors, head injuries, excessive exercise, chronic illness, heavy alcohol use, opioid medications, anabolic steroids, and conditions that cause iron overload can all suppress LH production. High levels of prolactin, another pituitary hormone, are another common culprit.
LH Testing and Fertility Tracking
Doctors measure LH through a simple blood test, often alongside FSH, to evaluate fertility, diagnose hormonal disorders, or confirm menopause. The timing of the blood draw matters for women, since LH fluctuates throughout the cycle.
Home ovulation predictor kits work by detecting the LH surge in urine. These kits are reasonably accurate: studies show they predict ovulation within one day of the actual surge about 82% to 88% of the time, and within two days about 89% to 96% of the time. For couples trying to conceive, a positive result on one of these kits signals that ovulation is likely within the next day or two, marking the most fertile window of the cycle.