Luteinizing Hormone (LH)
LH is produced by the pituitary and acts on the gonads. In women, the mid-cycle LH surge triggers ovulation (this is what ovulation kits detect). In men, LH stimulates testosterone production. Like FSH, high LH means gonads are failing, low LH means pituitary problem. Special pattern: high LH with normal/low FSH (elevated ratio) suggests PCOS. In men, LH is essential for classifying hypogonadism — high LH = testicular failure, low LH = pituitary problem (potentially treatable).
Luteinizing hormone (LH) is a critical reproductive hormone produced by the pituitary gland. In women, the mid-cycle LH surge triggers ovulation — the release of an egg from the ovary. In men, LH stimulates the testes to produce testosterone. Together with FSH, LH forms the hormonal command system that drives reproductive function in both sexes.
Why does this matter? LH testing helps evaluate a wide range of reproductive concerns. In women, it helps assess ovulation, diagnose causes of irregular periods, evaluate fertility, and confirm menopause. The LH-to-FSH ratio provides clues about conditions like polycystic ovary syndrome (PCOS). In men, LH helps distinguish between different causes of low testosterone — whether the problem is in the testes or the pituitary gland. This distinction fundamentally changes treatment approach.
Key Benefits of Testing
LH testing provides essential information about reproductive health. In women, it helps confirm ovulation, evaluate menstrual irregularities, diagnose PCOS (where LH is often elevated relative to FSH), and assess ovarian function. In men, LH is crucial for evaluating low testosterone — high LH with low testosterone indicates testicular failure, while low LH with low testosterone points to pituitary problems.
Because LH and FSH work as partners, testing both together provides a more complete picture than either alone. Their ratio and combined pattern help pinpoint the source of reproductive dysfunction.
What Does This Test Measure?
The LH test measures the concentration of luteinizing hormone in your blood. Like FSH, LH is a gonadotropin — a hormone produced by the pituitary gland that acts on the gonads (ovaries or testes). The hypothalamus controls LH release through gonadotropin-releasing hormone (GnRH).
How LH Works in Women
LH has two main roles in the female reproductive cycle. First, it contributes to follicle development alongside FSH during the first half of the cycle. Second — and most dramatically — the mid-cycle LH surge triggers ovulation. When estradiol from the mature follicle reaches a threshold level, it triggers a massive release of LH from the pituitary. This LH surge causes the dominant follicle to rupture and release its egg within 24-36 hours.
After ovulation, LH stimulates the ruptured follicle to transform into the corpus luteum, which produces progesterone to support a potential pregnancy.
LH levels vary significantly through the menstrual cycle. They’re relatively low in the follicular and luteal phases, with a dramatic spike at mid-cycle that lasts only 24-48 hours. This spike is what ovulation predictor kits detect in urine.
How LH Works in Men
In men, LH acts on Leydig cells in the testes, stimulating them to produce testosterone. This is the primary hormonal signal for testosterone production. Unlike women, men don’t have cyclical LH patterns — levels remain relatively stable, with minor fluctuations throughout the day.
Testosterone provides negative feedback to the pituitary, suppressing LH release when testosterone levels are adequate. When testosterone is low, the pituitary releases more LH trying to stimulate the testes. This feedback relationship makes LH essential for interpreting testosterone results.
The LH-FSH Partnership
LH and FSH work together but have different primary targets. FSH mainly drives follicle development (in women) and sperm production (in men). LH mainly triggers ovulation and progesterone production (in women) and testosterone production (in men). Evaluating both hormones together reveals more than either alone — their ratio and combined levels help diagnose specific conditions.
Why This Test Matters
For Women
Confirms ovulation. Detection of the LH surge confirms ovulation is about to occur. This is the basis of ovulation predictor kits used for timing intercourse. Blood LH testing can confirm ovulatory cycles when other signs are unclear.
Helps diagnose PCOS. Polycystic ovary syndrome often shows elevated LH with normal or low FSH, creating a high LH-to-FSH ratio. While this ratio alone doesn’t diagnose PCOS, it’s a supportive finding. Elevated LH contributes to the excess androgen production seen in PCOS.
Evaluates menstrual irregularities. LH levels help determine why periods are irregular or absent. High LH and FSH indicate ovarian failure. Low LH and FSH suggest hypothalamic or pituitary dysfunction. Abnormal LH-to-FSH ratio may point toward PCOS.
Confirms menopause and ovarian failure. Persistently elevated LH and FSH with low estradiol confirms menopause or premature ovarian insufficiency.
For Men
Classifies hypogonadism. When testosterone is low, LH distinguishes primary from secondary hypogonadism. Primary hypogonadism (testicular failure) shows high LH — the pituitary is trying to stimulate testes that can’t respond. Secondary hypogonadism (pituitary/hypothalamic failure) shows low or normal LH — the testes aren’t receiving adequate stimulation.
Guides treatment decisions. The type of hypogonadism determines treatment. Primary hypogonadism typically requires testosterone replacement since the testes can’t produce more. Secondary hypogonadism may respond to treatments that stimulate the pituitary or provide LH-like hormones, potentially preserving fertility.
Evaluates infertility. LH is part of male fertility evaluation, helping assess the hormonal environment for sperm production.
Value of Testing
LH is most powerful when interpreted with FSH, testosterone (in men), and estradiol (in women). The combined pattern tells the story of the entire reproductive axis — from the hypothalamus and pituitary down to the gonads.
For women with irregular cycles or concerns about fertility, early LH testing can identify patterns like PCOS before they complicate conception attempts. For men experiencing fatigue or decreased libido, LH alongside testosterone distinguishes between testicular and pituitary causes — information that shapes treatment choices and potentially preserves fertility options.
What Can Affect LH Levels?
Causes of High LH in Women
- Mid-cycle ovulation surge — normal and temporary
- Menopause — persistently elevated
- Premature ovarian insufficiency
- Polycystic ovary syndrome (elevated relative to FSH)
- Primary ovarian failure from any cause
- Turner syndrome and other genetic conditions
Causes of Low LH in Women
- Hypothalamic amenorrhea from stress, low weight, or excessive exercise
- Pituitary disorders affecting gonadotropin production
- Hyperprolactinemia — elevated prolactin suppresses LH
- Pregnancy — LH is suppressed
- Hormonal contraceptives — suppress pituitary gonadotropins
- Kallmann syndrome — genetic GnRH deficiency
Causes of High LH in Men
- Primary testicular failure — testes can’t produce testosterone despite stimulation
- Klinefelter syndrome (XXY)
- Testicular damage from infection, trauma, radiation, or chemotherapy
- Age-related testicular decline
- Anorchia (absent testes)
Causes of Low LH in Men
- Pituitary disorders — tumors, surgery, radiation
- Hypothalamic dysfunction
- Kallmann syndrome
- Hyperprolactinemia
- Anabolic steroid use — strongly suppresses LH
- Opioid use — suppresses the hypothalamic-pituitary axis
- Severe obesity — can suppress gonadotropins
- Severe illness or malnutrition
Timing Considerations
In women, LH varies dramatically with the menstrual cycle. Baseline testing (days 2-4) assesses tonic LH levels. Mid-cycle testing may capture the ovulation surge if timing is right, but this surge is brief and easily missed with random blood testing — urine-based ovulation kits are more practical for detecting the surge.
In men, LH has minor fluctuations but no major cycle. Morning testing is often preferred due to slight diurnal variation.
When Should You Get Tested?
For Women
Irregular or absent periods: LH and FSH together help identify the cause — ovarian failure versus hypothalamic/pituitary dysfunction versus PCOS.
Suspected PCOS: Elevated LH relative to FSH supports the diagnosis alongside other criteria.
Fertility evaluation: LH is part of the hormonal workup for infertility.
Confirming menopause: Elevated LH and FSH with low estradiol confirms menopausal status.
Evaluating ovulation: When there’s uncertainty about whether ovulation is occurring.
For Men
Low testosterone symptoms: Fatigue, low libido, erectile dysfunction, decreased muscle mass. LH determines if the problem is testicular or pituitary.
Infertility evaluation: LH helps assess the hormonal support for sperm production.
Suspected hypogonadism: Essential for classifying the type and guiding treatment.
Delayed puberty: In adolescents, helps evaluate whether delayed puberty is constitutional or pathological.
Understanding Your Results
LH interpretation requires context — sex, age, menstrual cycle timing (for women), symptoms, and other hormone levels. The pattern of LH with FSH and sex hormones tells the story.
For Premenopausal Women
High LH with high FSH and low estradiol indicates ovarian failure — menopause or premature ovarian insufficiency. The pituitary is maximally stimulating ovaries that can’t respond.
High LH with normal/low FSH (elevated LH:FSH ratio) suggests PCOS. This pattern, especially with a ratio greater than 2:1, supports the diagnosis when combined with other clinical features.
Low LH with low FSH indicates hypothalamic or pituitary dysfunction. The ovaries aren’t receiving adequate stimulation. Causes include stress, low weight, excessive exercise, pituitary tumors, or elevated prolactin.
Very high LH (mid-cycle surge) is normal if timed around ovulation. This brief spike triggers egg release.
For Postmenopausal Women
LH is persistently elevated after menopause, similar to FSH. This reflects absent ovarian hormone production and loss of negative feedback.
For Men
High LH with low testosterone indicates primary hypogonadism — testicular failure. The pituitary is working overtime to stimulate testes that can’t produce adequate testosterone.
Low or normal LH with low testosterone indicates secondary hypogonadism — the problem is at the pituitary or hypothalamus. The testes could potentially produce testosterone if properly stimulated.
Normal LH with normal testosterone suggests the hypothalamic-pituitary-gonadal axis is functioning normally.
What to Do About Abnormal Results
For High LH in Women
If FSH is also high with low estradiol, this confirms ovarian failure. In young women, evaluate for premature ovarian insufficiency with additional testing. Hormone replacement is typically recommended.
If LH is elevated with normal/low FSH (high LH:FSH ratio), evaluate for PCOS with ultrasound and androgen levels. Management addresses symptoms and long-term metabolic risks.
For Low LH in Women
Check prolactin — hyperprolactinemia is a treatable cause of low LH.
Evaluate for hypothalamic amenorrhea — assess stress, body weight, and exercise patterns. Lifestyle modification often restores normal function.
Consider pituitary imaging if other causes are excluded or additional pituitary hormones are abnormal.
For High LH in Men
Confirm with testosterone level. High LH with low testosterone confirms primary hypogonadism.
Evaluate underlying cause — genetic testing (karyotype for Klinefelter syndrome), testicular ultrasound, history of testicular injury or infection.
Treatment typically involves testosterone replacement, though this doesn’t restore fertility.
For Low LH in Men
Evaluate other pituitary hormones — low LH may be part of broader pituitary dysfunction.
Pituitary MRI may be indicated to evaluate for tumors.
Review medications — opioids and anabolic steroids commonly suppress LH.
Treatment options may include addressing underlying causes. For fertility, gonadotropin therapy can stimulate testosterone and sperm production when the testes are capable of responding.
Related Health Conditions
Polycystic Ovary Syndrome (PCOS)
PCOS frequently shows elevated LH with normal or low FSH, creating a high LH-to-FSH ratio. Excess LH stimulates ovarian androgen production, contributing to symptoms like acne, hirsutism, and irregular periods. The elevated LH also disrupts normal follicle development and ovulation.
Premature Ovarian Insufficiency
When ovaries fail before age 40, both LH and FSH rise as the pituitary tries to stimulate unresponsive ovaries. Elevated gonadotropins with low estradiol confirm the diagnosis. The condition causes infertility and requires hormone replacement to prevent long-term complications.
Menopause
At menopause, LH rises and remains persistently elevated along with FSH. This reflects the loss of ovarian function and absence of hormone feedback. Testing confirms menopausal status when symptoms are ambiguous.
Hypothalamic Amenorrhea
When stress, low body weight, or excessive exercise suppresses the hypothalamus, both LH and FSH production decrease. Without adequate gonadotropin stimulation, the ovaries don’t function normally, causing absent periods. Unlike ovarian failure, this is potentially reversible with lifestyle changes.
Male Hypogonadism
LH is essential for classifying male hypogonadism. Primary hypogonadism (testicular failure) shows high LH — the pituitary is working but testes can’t respond. Secondary hypogonadism (pituitary/hypothalamic failure) shows low LH — the testes could work if stimulated. This distinction determines treatment approach and fertility options.
Pituitary Disorders
Pituitary tumors, surgery, or other conditions can impair LH production, causing secondary hypogonadism. Low LH leads to low testosterone in men and ovulatory dysfunction in women. Identifying pituitary problems is important because they may be treatable and can affect other pituitary hormones as well.
Kallmann Syndrome
This genetic condition involves deficiency of GnRH, resulting in low LH and FSH. Affected individuals don’t undergo normal puberty without treatment. The condition is often associated with absent or reduced sense of smell. Gonadotropin therapy can induce puberty and potentially restore fertility.
Related Biomarkers Often Tested Together
FSH (Follicle-Stimulating Hormone) — Partner gonadotropin; LH and FSH together assess the complete pituitary-gonad axis.
Estradiol — In women, interpreted with LH to assess ovarian function.
Testosterone — In men, the key hormone LH stimulates; their relationship classifies hypogonadism.
Progesterone — Elevated in the luteal phase confirms ovulation occurred after LH surge.
Prolactin — Elevated prolactin suppresses LH; important to check in hypogonadism evaluation.
AMH — Additional ovarian reserve marker that complements gonadotropin assessment.
Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.
Frequently Asked Questions
Luteinizing hormone is produced by the pituitary gland. In women, the LH surge triggers ovulation. In men, LH stimulates the testes to produce testosterone. LH works with FSH to regulate reproductive function.
Rising estradiol from the maturing follicle triggers the LH surge. When estradiol reaches a threshold level, it switches from suppressing LH to stimulating a massive release. This surge causes ovulation within 24-36 hours.
Both are pituitary gonadotropins, but they have different primary functions. FSH mainly stimulates follicle development and sperm production. LH mainly triggers ovulation and testosterone production. Testing both together provides the most complete picture.
A high LH-to-FSH ratio (greater than 2:1) is often seen in PCOS. Normally, FSH is higher than or equal to LH. An elevated ratio suggests altered pituitary signaling that contributes to PCOS pathophysiology.
LH is the primary signal for testosterone production. Low testosterone with high LH means the testes are failing despite stimulation. Low testosterone with low LH means the pituitary isn’t sending adequate signals — a potentially treatable situation.
The LH surge occurs 24-36 hours before ovulation. Ovulation predictor kits detect this surge in urine. Blood LH testing can identify the surge but is less practical due to timing — the surge is brief and easily missed with random testing.
Yes. After menopause, LH rises and stays elevated because the ovaries no longer produce hormones that suppress it. Elevated LH with elevated FSH and low estradiol confirms menopause.
References
Key Sources:
- Practice Committee of the American Society for Reproductive Medicine. Current evaluation of amenorrhea. Fertil Steril. 2008;90(5 Suppl):S219-225.
- Bhasin S, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744.
- Teede HJ, et al. Recommendations from the international evidence-based guideline for the assessment and management of polycystic ovary syndrome. Hum Reprod. 2018;33(9):1602-1618.
