Luteinizing Hormone

LH (luteinizing hormone) is a hormone your pituitary gland releases to tell the gonads, the testicles in men and the ovaries in women, how much sex hormone to make. The number is close to meaningless by itself. Paired with a testosterone or estradiol result, it tells you where a hormone problem sits: in the gland that makes the hormone, or in the pituitary signal that should be driving it.

What is LH (luteinizing hormone)?

LH is one of two gonadotropins, hormones that act on the gonads, made by the anterior pituitary (the front part of the pituitary gland, which sits just under the brain). The other gonadotropin is FSH (follicle-stimulating hormone). Above the pituitary, the hypothalamus releases GnRH (gonadotropin-releasing hormone) in pulses, and those pulses tell the pituitary to send out LH in pulses of its own. ²

In men, LH travels to the Leydig cells inside the testicles and tells them to make testosterone. In women, LH works with FSH across the menstrual cycle and produces the mid-cycle surge that releases an egg. Sex hormones and a gonad protein called inhibin feed back to the pituitary, turning LH up when their levels fall and down when they rise. ²

What does a high LH level mean?

A high LH usually means the pituitary is shouting at a gland that is not answering. When the testicle or ovary stops making enough sex hormone, the feedback brake comes off and the pituitary pushes out more LH to compensate. So a high LH sitting next to a low sex hormone points to the gland itself. ¹

In a man, low testosterone with a high LH (and usually a high FSH) is primary hypogonadism: the testicles are failing. Common causes include Klinefelter syndrome (an extra X chromosome), prior chemotherapy or radiation, mumps that inflamed the testes, injury, and aging testes. ¹

In a woman, a persistently high LH and FSH with a low estradiol is the biochemical picture of menopause or, before age 40, primary ovarian insufficiency (the ovaries winding down early). ³

What does a low LH level mean?

A low LH, or an LH that sits in the normal range while the sex hormone is clearly low, means the pituitary is not sending the order it should. This is secondary (also called central) hypogonadism: the gland could work, but the signal is not reaching it. In a man, it shows up as low testosterone with a low or normal LH and FSH. Clinicians call a normal LH in this setting an inappropriately normal LH, because the pituitary should be pushing harder. ¹

Causes include a pituitary tumor or other pituitary damage, a high level of the hormone prolactin (which suppresses GnRH), opioid painkillers, anabolic steroids or testosterone taken from outside the body (which switch off the body's own signal), severe illness, large weight loss or overtraining, and rare inherited GnRH deficiency. ¹

LH and FSH: read as a pair

LH and FSH are the two gonadotropins, and labs almost always run them together because they answer different halves of the same question. LH tracks most closely with sex-hormone production, testosterone in men and the ovulation trigger in women, while FSH tracks with sperm production in men and the egg supply in women. When a gland fails, both usually rise; when the signal fails, both usually fall. ¹

We suggest measuring serum LH and FSH concentrations to distinguish between primary and secondary hypogonadism.Endocrine Society Clinical Practice Guideline (Bhasin et al., JCEM 2018)

LH and the menstrual cycle

Across a menstrual cycle, LH stays low through the first half while a follicle grows, then spikes sharply around day 12 to 14. That LH surge is what releases the egg, with ovulation following roughly 24 to 36 hours later. Home ovulation predictor kits work by catching that surge in urine. ²

LH and PCOS: what the ratio does and doesn't tell you

Many women with PCOS (polycystic ovary syndrome) have an LH that runs higher than their FSH, so a raised LH-to-FSH ratio is common in PCOS. It is not a diagnostic test. The 2023 international PCOS guideline recommends against using LH, FSH, or their ratio to diagnose PCOS. ⁴

What is a normal LH level?

LH is measured in international units per liter (IU/L). There is no single normal number, because it depends on sex and, in women, the phase of the menstrual cycle. Ranges are also assay-specific (the number depends on which lab test was run), so read your result against your own lab's reference range printed next to it. ² The typical bands below come from a laboratory reference. ⁵

How LH is tested

• It is a simple blood draw, usually from a vein in your arm. LH itself does not need fasting, though it is often drawn with other tests that ask for a morning or fasting sample.
• In men, one morning sample is usually enough, ideally drawn with testosterone and FSH. Because testosterone is released in bursts (pulsatile) and highest in the morning, morning draws are standard.
• In women, timing matters. For a cycle workup, LH and FSH are often drawn on day 2 to 4 of the period; to confirm ovulation, LH is tracked around mid-cycle.
• LH is rarely ordered alone. It travels with FSH, and with testosterone in men or estradiol in women, because the pattern is what gets read.
• It is a common, inexpensive test, usually covered when there is a medical reason such as low libido, irregular periods, infertility, or symptoms of low testosterone. Coverage for screening without symptoms varies.

Who should get LH checked, and when to retest

LH is worth checking when symptoms point to a hormone problem: in men, low libido, fatigue, erectile difficulty, or small testes; in women, absent or irregular periods, trouble conceiving, or menopausal symptoms before 40. It also helps sort out an already-abnormal testosterone or estradiol by showing whether the gland or the signal is at fault. Because a single value can be thrown off by illness, poor sleep, or timing, an abnormal result is usually repeated, often a few weeks later, before conclusions are drawn, and in women a cycle-timed redraw is common. Your clinician sets the exact timing based on the cause. ¹

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