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LH Blood Test: Luteinizing Hormone Levels & the Ovulation Surge

LH blood test explained: luteinizing hormone levels in mIU/mL by cycle phase, the LH surge that triggers ovulation, the LH:FSH ratio in PCOS, and high vs low results.

Published July 18, 202613 min readWritten by the Blood Analysis Team · Reviewed and verified by Julien Priour

The LH blood test measures luteinizing hormone, one of the two gonadotropins your pituitary gland sends to the ovaries or testes. In women, a sharp mid-cycle surge of LH is the trigger that releases the egg — the very signal that home ovulation predictor kits detect in urine. In men, LH tells the testes to make testosterone. Clinicians order an LH test to work up irregular periods, fertility problems, polycystic ovary syndrome (PCOS), suspected menopause, low testosterone, and early or delayed puberty. This guide explains what luteinizing hormone does, the normal LH range in mIU/mL by cycle phase, and how to read a high or low result. LH is almost never interpreted alone — it belongs to the hormone panel, read alongside FSH and estradiol.

Key takeaways

  • LH is a gonadotropin made by the pituitary; its mid-cycle surge triggers ovulation in women, and it drives testosterone production in men.123
  • Levels swing widely across the menstrual cycle — low in the follicular phase, a dramatic ovulatory peak, then the luteal phase — so timing of the draw matters enormously.45
  • The unit is mIU/mL (identical to IU/L). Reference ranges are lab- and assay-specific — always read the range printed on your report.15
  • LH is interpreted with FSH and estradiol (and, in men, testosterone); the combination points to a diagnosis, not any single number.6
  • A high LH:FSH ratio is common in PCOS but is not a diagnostic criterion.789
  • High LH + high FSH points to the gonad itself (menopause, ovarian or testicular failure); low LH with low sex hormones points to the pituitary or hypothalamus.1011

What is LH?

Luteinizing hormone (LH) is secreted by the anterior pituitary gland, under the command of the brain's hypothalamus, which releases pulses of gonadotropin-releasing hormone (GnRH). Together with follicle-stimulating hormone (FSH), LH forms the hypothalamic-pituitary-gonadal (HPG) axis — the loop that governs reproduction.32

Its jobs differ by sex:

  • In women, LH works with FSH through the menstrual cycle. As a follicle matures and pours out estradiol late in the follicular phase, that rising estradiol flips the pituitary from braking LH to releasing it — producing a sudden LH surge that triggers ovulation. Afterward, LH sustains the corpus luteum, the structure that makes progesterone to prepare the uterine lining.41
  • In men, LH stimulates the Leydig cells of the testes to produce testosterone — a steady signal rather than a monthly surge.32

Because LH rises and falls with the cycle and moves in lockstep with FSH and estradiol, a single LH value in isolation says very little. It is the pattern across markers that carries the meaning.6

Why the test is done

A clinician typically orders an LH blood test to:1126

  • work up irregular, absent, or abnormal periods (oligomenorrhea, amenorrhea) or trouble conceiving;
  • help evaluate infertility and confirm whether ovulation is occurring, as part of a fertility assessment;9
  • assess suspected PCOS, alongside androgens and ultrasound or AMH;7
  • investigate menopause or primary ovarian insufficiency when periods stop early;
  • in men, evaluate low testosterone / hypogonadism and locate whether the problem is in the testes or the pituitary;10
  • assess early (precocious) or delayed puberty in children, where LH is a key marker of when the reproductive axis has switched on.13

Because ovulatory disorders are common and heterogeneous, an international framework — the FIGO ovulatory disorders classification — sorts their causes into hypothalamic, pituitary, and ovarian groups, and LH and FSH help place a patient within it.14

The LH surge and ovulation

The single most useful thing LH does clinically is mark ovulation. For most of the follicular phase LH stays low. Then, as the dominant follicle drives estradiol past a threshold, the pituitary releases a brief, dramatic surge — LH can climb many-fold over a day or two. That surge is the trigger: ovulation follows roughly 24 to 36 hours later.41

This is exactly why home ovulation predictor kits work. They detect the LH surge in urine; a positive result signals that the fertile window has opened and ovulation is imminent. At the neuroendocrine level, a specialized population of kisspeptin neurons in the hypothalamus generates the LH pulses and the pre-ovulatory surge — a mechanism now central to fertility research.4

A blood LH test can serve the same purpose in a clinical setting, and when paired with estradiol and a mid-luteal progesterone, it helps confirm that ovulation actually happened and characterize a cycle disorder. Because the surge is short-lived, a single random draw can easily miss it — which is why timing, and the combination of markers, matter so much.

How the test is done

The LH test is a routine blood draw from a vein in the arm; no fasting is required.1 What matters far more than fasting is timing within the cycle. For a baseline in a menstruating woman, the sample is often drawn in the early follicular phase (around cycle days 2–4), together with FSH and estradiol. If the goal is to capture the ovulatory surge, serial samples timed to mid-cycle may be used instead.69

Tell your clinician the first day of your last period, your cycle length, and any hormonal contraception or fertility medication — all of which change how the result is read. In men and in children, timing is less about the cycle, but the same rule applies: LH is interpreted alongside the other gonadotropins and sex hormones, not on its own.6

Normal ranges

Below are indicative adult reference values in mIU/mL (equivalent to IU/L). In women they depend heavily on the phase of the cycle; postmenopausal and male ranges are steadier. Reference intervals vary by laboratory and assay, so always defer to the range on your report.51

SituationIndicative LH (mIU/mL)
Woman — follicular phase~ 1.9 – 12.5
Woman — mid-cycle (ovulatory) peak~ 8.7 – 76
Woman — luteal phase~ 0.5 – 16.9
Postmenopausal~ 5 – 52 (elevated)
Adult man~ 1.5 – 9.3
Children (prepubertal)very low (often < 0.3)

Good to know: the unit is mIU/mL, numerically identical to IU/L. The ovulatory peak is brief and easily missed depending on the day of the draw — the same LH surge that home ovulation kits detect. As with FSH, the timing of the sample is decisive, and a single value means little without FSH, estradiol, and your clinical context.54

High LH

A high LH is interpreted mainly by what FSH is doing at the same time.

  • High LH and high FSH usually means the gonad itself is failing to respond, so the pituitary pushes harder. In women this is the hallmark of menopause and primary ovarian insufficiency; in men it points to primary (testicular) hypogonadism.105 After menopause, gonadotropins stay persistently elevated — but the diagnosis of menopause remains clinical (12 months without a period), and AMH predicts its timing better than LH or FSH.1516
  • High LH with a high LH:FSH ratio is a classic (though inconstant) finding in PCOS, where LH is often disproportionately elevated relative to FSH — see below.
  • A transient high LH can simply reflect the mid-cycle surge — a normal, expected spike if the sample was drawn around ovulation.

In children, an LH that rises into the pubertal range before the expected age is a central marker of central precocious puberty, meaning the HPG axis has activated early — a finding that warrants pediatric endocrinology evaluation.13

Low LH

A low LH — or one that is "inappropriately normal" while sex hormones are low — points upstream, to the pituitary or hypothalamus, rather than the gonad. This pattern (low LH, low FSH, low estradiol or testosterone) is called secondary (central) hypogonadism or hypogonadotropic hypogonadism.1011

Common causes include:

  • Functional hypothalamic amenorrhea (FHA) in women — the axis is suppressed by low energy availability, significant weight loss, intense exercise, or chronic stress, a frequent and often reversible cause of low LH with absent periods, addressed in a dedicated Endocrine Society guideline.11
  • Pituitary disorders, such as a pituitary tumor, or high prolactin, which suppresses GnRH pulses;
  • Certain medications and the hormonal changes of pregnancy or lactation;
  • In men, central hypogonadism from pituitary or hypothalamic causes, which LH and FSH help distinguish from testicular failure.10

Because a low LH is only meaningful when the sex hormones it controls are also low, this is another situation where the whole panel, not the LH number alone, drives the interpretation.

The LH:FSH ratio in PCOS

In polycystic ovary syndrome, LH is frequently elevated relative to FSH, giving a high LH:FSH ratio (often cited around 2:1 or higher). This reflects altered GnRH pulse frequency in PCOS. It is a suggestive finding — but it is explicitly not a diagnostic criterion.78

The 2023 International Evidence-based Guideline for PCOS diagnoses the condition using the Rotterdam criteria — a combination of irregular cycles / ovulatory dysfunction, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound or an elevated AMH in adults — with no role for the LH:FSH ratio as a diagnostic test.79 A study evaluating the ratio's diagnostic performance likewise found it far less discriminating than AMH or androgens.8 In short: a high ratio can raise suspicion, but PCOS is diagnosed by criteria, not by LH.

Factors that affect the result

Several ordinary factors move LH or its interpretation, with no disease present:165

  • Cycle timing. The single biggest factor in women — the same LH reads very differently in the follicular phase, at the ovulatory peak, or in the luteal phase.
  • Hormonal contraception. The pill and other hormonal methods suppress LH; a result on contraception does not reflect your baseline axis.
  • Menopausal status. Gonadotropins rise substantially after menopause.
  • Pregnancy and breastfeeding, which alter the reproductive axis.
  • Medications, including GnRH agonists/antagonists, fertility drugs, and anything that raises prolactin.
  • A missed surge. Because the ovulatory peak is brief, a single random draw may catch — or miss — it entirely.

Always tell your clinician your cycle day, contraceptive use, medications, and any chance of pregnancy.

When to see a doctor

Order and interpret an LH test with a clinician, not on your own. It's worth a medical review if you have irregular or absent periods, are struggling to conceive, have symptoms of low testosterone (low libido, fatigue, erectile dysfunction) in men, signs of early or delayed puberty in a child, or a result that falls outside your lab's range. An isolated, mildly abnormal LH is rarely alarming by itself — what matters is the pattern with FSH, estradiol or testosterone, your symptoms, and your history. See the hormone panel for how these markers fit together.

Recent research

According to recent publications indexed on PubMed:

  • The neuroscience of the LH surge. Research on kisspeptin neurons has clarified how the hypothalamus generates LH pulses and the pre-ovulatory surge that triggers ovulation — an active target for understanding and treating infertility.4
  • PCOS: the LH:FSH ratio is not a criterion. The 2023 international guideline confirms a diagnosis built on the Rotterdam criteria (with AMH as an alternative to ultrasound in adults), and does not adopt the LH:FSH ratio as a diagnostic test.7 A diagnostic-performance study found the ratio inferior to AMH and androgens.8
  • A framework for ovulatory disorders. The FIGO classification gives a standardized structure — hypothalamic, pituitary, ovarian — for interpreting LH and FSH within a fertility work-up.14
  • Menopause is a clinical diagnosis. Gonadotropins rise, but the decision rests on clinical criteria; AMH is the better predictor of menopausal timing, and management of early menopause has its own evidence base.1516
  • Functional hypothalamic amenorrhea. A leading cause of low LH in younger women (from low energy availability, weight loss, or intense exercise), FHA has a dedicated Endocrine Society guideline for diagnosis and management.11
  • Localizing male hypogonadism. LH and FSH remain essential to separate primary (testicular) hypogonadism from secondary (central) causes when evaluating low testosterone.10

These findings concern diagnosis and monitoring; they do not authorize any self-treatment and do not replace your physician's advice.

Get your LH interpreted by AI DiagMe

LH is never read alone: its meaning depends on your FSH, estradiol or testosterone, the day of your cycle, and your whole context — see the hormone panel. That cross-reading is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole context into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

What is an LH blood test used for?
It measures luteinizing hormone, a pituitary gonadotropin. In women its mid-cycle surge triggers ovulation; in men it drives testosterone. The test helps evaluate irregular periods, infertility, PCOS, menopause, low testosterone, and early or delayed puberty — always read alongside FSH and estradiol or testosterone.
What is a normal LH level?
The unit is mIU/mL (= IU/L). In women it depends on the cycle: roughly 1.9–12.5 in the follicular phase, 8.7–76 at the ovulatory peak, and 0.5–16.9 in the luteal phase. Adult men run about 1.5–9.3, and postmenopausal women are elevated (~5–52). Ranges vary by lab, so use the one on your report.
Can an LH test detect ovulation?
Yes. The LH surge precedes ovulation by about 24–36 hours, and it's exactly what home ovulation predictor kits detect in urine. A blood LH test, paired with estradiol and progesterone, can help confirm that ovulation occurred and characterize a cycle disorder.
What is the LH:FSH ratio, and does it diagnose PCOS?
It's the ratio between the two gonadotropins, often elevated in PCOS. It is suggestive but not diagnostic: PCOS is diagnosed by the Rotterdam criteria (irregular cycles, hyperandrogenism, and polycystic morphology or high AMH), not by the ratio.
What does a high LH mean?
With a high FSH too, it usually signals a gonad that isn't responding — menopause, primary ovarian insufficiency, or testicular failure in men. In PCOS, LH may be high with a raised LH:FSH ratio. In a child, an early rise into the pubertal range suggests central precocious puberty. Only a clinician can place the result in context.
What does a low LH mean?
A low LH with low sex hormones points upstream — to the pituitary or hypothalamus (central hypogonadism). A common, often reversible cause in women is functional hypothalamic amenorrhea from low energy availability, weight loss, or intense exercise.

Bottom line

The LH blood test measures a pituitary gonadotropin whose mid-cycle surge triggers ovulation in women and whose steady signal drives testosterone in men. Levels swing across the menstrual cycle, the unit is mIU/mL, and the number only makes sense with FSH, estradiol, and your clinical picture. High LH with high FSH points to the gonad (menopause, ovarian or testicular failure); low LH points to the pituitary or hypothalamus; a high LH:FSH ratio suggests but does not diagnose PCOS. No value is read alone — it's your full set of markers and your profile that gives it meaning, exactly what AI DiagMe does, alongside your physician. See the hormone panel for the bigger picture.

Sources

Official U.S. sources and peer-reviewed publications (PubMed) used for this guide:

Footnotes

  1. MedlinePlus (U.S. National Library of Medicine, NIH) — Luteinizing Hormone (LH) Levels Test. medlineplus.gov ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8

  2. Endocrine Society — Luteinizing Hormone (Hormone Health Network). hormone.org ↩ ↩2 ↩3

  3. Kaprara A, Huhtaniemi IT. The hypothalamus-pituitary-gonad axis: Tales of mice and men. Metabolism, 2018. PubMed · DOI ↩ ↩2 ↩3

  4. Stevenson H, et al. Kisspeptin-neuron control of LH pulsatility and ovulation. Front Endocrinol (Lausanne), 2022. PubMed · DOI ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  5. Mayo Clinic Laboratories — Luteinizing Hormone (LH), Serum (reference values). mayocliniclabs.com ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  6. Testing.com — Luteinizing Hormone (LH) Test. testing.com ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  7. Teede HJ, et al. Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab, 2023. PubMed · DOI ↩ ↩2 ↩3 ↩4 ↩5

  8. Alhassan S, et al. Diagnostic Performance of Anti-Müllerian Hormone, LH/FSH Ratio, Testosterone, and Prolactin to Predict Polycystic Ovary Syndrome. Int J Womens Health, 2023. PubMed · DOI ↩ ↩2 ↩3 ↩4

  9. American College of Obstetricians and Gynecologists (ACOG) — Polycystic Ovary Syndrome (PCOS). acog.org ↩ ↩2 ↩3 ↩4

  10. Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab, 2018. PubMed · DOI ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  11. Gordon CM, Ackerman KE, et al. Functional Hypothalamic Amenorrhea: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab, 2017. PubMed · DOI ↩ ↩2 ↩3 ↩4

  12. Cleveland Clinic — Luteinizing Hormone. my.clevelandclinic.org ↩

  13. MedlinePlus (NIH) — Central Precocious Puberty. medlineplus.gov ↩ ↩2

  14. Munro MG, Balen AH, et al. The FIGO ovulatory disorders classification system. Int J Gynaecol Obstet, 2022. PubMed · DOI ↩ ↩2

  15. Mishra GD, Davies MC, et al. Optimising health after early menopause. Lancet, 2024. PubMed · DOI ↩ ↩2

  16. Nelson SM, Davis SR, et al. Anti-Müllerian hormone for the diagnosis and prediction of menopause: a systematic review. Hum Reprod Update, 2023. PubMed · DOI ↩ ↩2

Medical disclaimer. This article is provided for informational and educational purposes only; it is not medical advice and does not replace a consultation. Reference ranges vary by laboratory and method: only your physician can interpret your results in your specific context.