Luteinizing Hormone (LH)

In a menstruating woman the cycle day moves the expected value far more than the pulses do, so an LH drawn without a recorded cycle day is hard to read at all. Postmenopausal and male levels are steadier, but even then the localizing logic needs a partner hormone beside it.

A high LH means the pituitary is sending a strong signal, and the reason comes from reading what the gonad did with it. The headline cause is the most ordinary one: menopause. As the ovaries release fewer eggs and make less estrogen, the brake on the pituitary lifts, and LH and FSH climb to push harder. MedlinePlus notes that for a woman aged 45 or older, a high LH or FSH is usually a sign of normal perimenopause or menopause and often needs no testing at all.

Before that age, a persistently high LH with low estrogen is the pattern that earns a workup, because it can signal primary ovarian insufficiency, where the ovaries stop working early. In men, a high LH alongside a low testosterone is the signature of a problem at the testes: the beacon is at full power, but the gland below cannot answer. Causes include prior injury, certain infections, and genetic conditions. This is primary hypogonadism, and the high LH is what distinguishes it from the central kind.

There is one more high-LH pattern, and it is not a failing gland. In polycystic ovary syndrome, LH is often raised relative to FSH, tilting the LH:FSH ratio upward. NICHD describes elevated androgens as a defining feature of PCOS, and the disordered LH signal frequently sits beneath the irregular cycles and the high androgens. The ratio is a supporting clue a doctor weighs alongside cycles, symptoms, and other hormones, and a normal ratio does not rule PCOS out.

A low LH means the signal is faint, and a low LH next to a low sex hormone is the central pattern: the lamp itself is dim. MedlinePlus describes a below-normal adult LH as usually a sign of a problem with the pituitary or the hypothalamus, where the order to the gonads is written. When LH and FSH both read low while testosterone or estradiol is also low, the gonad is willing but the message never arrived. This is secondary, or central, hypogonadism.

Not every low LH is a pituitary disease. The signal can be turned down by circumstances:

• Severe physical stress on the body: very low body weight, low energy availability, or heavy training can quiet the hypothalamus, sometimes until periods stop.
• A pituitary disorder such as a tumor, or the effects of treatment to the area.
• High prolactin, which suppresses the GnRH signal that drives LH.
• Certain medications, including hormone therapies that switch off the body's own signal on purpose.

The symptoms people notice when LH runs low trace back to the low sex hormone it fails to summon: in women, irregular or absent periods and difficulty conceiving; in men, low libido, fatigue, and reduced muscle. They are read with that sex hormone, not off the LH number alone.

LH is one line on a hormone panel, and it reads best beside the markers that give it meaning. FSH is its constant partner, made by the same cells but doing a different job: FSH grows the follicle through the first half of the cycle, then the LH surge releases the egg, while in the testes LH drives testosterone and FSH supports sperm. In men, testosterone is the answer LH demands, and the LH versus testosterone comparison shows how the two together separate a testicular problem from a pituitary one. In women, LH is read against estradiol and progesterone across the cycle: the surge is what creates the corpus luteum whose progesterone confirms, about a week later, that ovulation actually happened. Like the gonadotropins, the gonadal feedback signal inhibin B is interpretable only as part of the set, since it falls as FSH climbs. The guide to reading a hormone panel shows how these lines assemble into one picture rather than a row of separate flags.

Because LH pulses through the day and swings across the cycle, a single value carries less weight than the same draw repeated under comparable conditions. A morning LH of 25 means one thing if it climbed steadily over two years and something quieter if it has held there all along, which is why a repeat or two often beats reading any one figure; the guide to how often to retest covers when a second draw is worth booking.