Hormone Journal

Luteinizing hormone

Also known as: LH

Medically reviewed by Hormone Journal Editorial Team · Last reviewed 2026-05-22

Luteinizing hormone (LH) is a pituitary glycoprotein that triggers ovulation in females and testosterone production in males, with levels rising up to 10-fold at mid-cycle.

What it is

Luteinizing hormone (LH) is a glycoprotein gonadotropin secreted by the anterior pituitary gland that triggers ovulation in females and drives testosterone synthesis in males, with mid-cycle LH surges rising 5- to 10-fold above baseline in people with ovaries. Also called lutropin, LH works in tandem with follicle-stimulating hormone (FSH) as one of the two principal regulators of the hypothalamic-pituitary-gonadal (HPG) axis. In Canada, LH is routinely measured through LifeLabs and Dynacare as part of fertility workups, menopause assessments, and investigations of hypogonadism in both sexes.

LH is a heterodimer composed of an alpha subunit (92 amino acids, shared with FSH, TSH, and hCG) and a hormone-specific beta subunit (121 amino acids). The combined molecule has a molecular mass of approximately 28 kDa. Gonadotroph cells — which make up 10–15% of the functional anterior pituitary — produce and release LH in response to pulsatile gonadotropin-releasing hormone (GnRH) from the hypothalamus.

Causes and mechanism

LH release is governed by the HPG axis through a feedback loop:

  1. The hypothalamus releases GnRH in pulses (roughly every 60–90 minutes in the follicular phase).
  2. GnRH binds gonadotroph receptors in the anterior pituitary, stimulating LH secretion.
  3. Rising estrogen and progesterone (females) or testosterone (males) feed back — mostly negatively — to suppress further GnRH and LH release.
  4. Exception: a sustained estrogen rise just before ovulation triggers a positive-feedback LH surge, the signal that causes follicle rupture and egg release.

In males, LH binds Leydig cells in the testes, stimulating testosterone synthesis. In females, LH drives steroidogenesis in theca cells and, at the mid-cycle surge, triggers ovulation and luteinization of the ruptured follicle into the corpus luteum.

LH reference ranges across life stages (approximate serum values)

Life stage / sexTypical LH range (IU/L)
Females — follicular phase2–15
Females — mid-cycle surge22–105
Females — luteal phase0.6–19
Postmenopausal females14–52
Adult males1.7–8.6
Prepubertal children< 0.3

Ranges vary by assay; always interpret against the reference interval provided by the testing laboratory (e.g., LifeLabs or Dynacare report).

Symptoms and diagnosis

Abnormal LH levels rarely cause symptoms on their own — it is the downstream hormonal consequences that patients notice.

Elevated LH is associated with primary gonadal failure (menopause, premature ovarian insufficiency, Klinefelter syndrome), polycystic ovary syndrome (PCOS — a condition where an elevated LH:FSH ratio, often greater than 2:1, reflects disordered gonadotropin pulsatility), and hypothalamic dysfunction from excessive exercise or low body weight.

Low LH points to hypothalamic or pituitary causes: Kallmann syndrome (a congenital GnRH deficiency often accompanied by anosmia), hyperprolactinemia, pituitary adenoma, or suppression from exogenous testosterone or anabolic steroids. Isolated LH deficiency is rare; it almost always co-occurs with FSH deficiency because both hormones originate from the same gonadotroph cells.

Clinically, LH is measured via serum immunoassay. Timing matters: a single random draw can be misleading given pulsatile secretion. Clinicians typically order LH alongside FSH, estradiol or testosterone, and prolactin to interpret the full HPG picture. Urine LH detection kits (ovulation predictor kits, available over the counter in Canada) detect the mid-cycle surge with reasonable accuracy for fertility tracking.

Treatment options

Treatment targets the underlying cause rather than LH itself.

  • LH deficiency causing infertility: Recombinant LH (lutropin alfa) or human menopausal gonadotropins (hMG, which contain both LH and FSH activity) are used in assisted reproduction protocols. Human chorionic gonadotropin (hCG) mimics the LH surge and is used to trigger ovulation in IVF cycles.
  • LH deficiency causing hypogonadism (not fertility-focused): Testosterone replacement therapy (males) or estrogen/progesterone therapy (females) corrects the downstream hormone deficit. These therapies are available through Canadian prescribers via in-person endocrinology or urology referral, or through virtual platforms such as Felix, Maple, Cleo, Phoenix, or others.
  • Elevated LH from PCOS: Lifestyle modification, combined oral contraceptives, or metformin can normalize gonadotropin ratios; GnRH agonists are used in some fertility protocols to suppress premature LH surges.
  • Elevated LH from menopause: Menopausal hormone therapy (MHT) suppresses elevated LH and FSH, though suppression of gonadotropins is not itself the therapeutic goal — symptom relief and long-term health outcomes are. The Society of Obstetricians and Gynaecologists of Canada (SOGC) 2021 menopause guidelines support MHT for eligible patients.

When to see a clinician in Canada

Seek assessment if you experience: irregular or absent periods, signs of premature ovarian insufficiency before age 40, unexplained infertility after 6–12 months of trying to conceive, symptoms of hypogonadism (low libido, fatigue, loss of muscle mass), or delayed puberty in an adolescent. A family physician can order an initial LH panel; complex cases are typically referred to a reproductive endocrinologist or general endocrinologist. Wait times for endocrinology in Canada vary widely by province — some patients use virtual-care services for initial assessment while awaiting specialist referral.

Limitations and open questions

Research is still emerging on LH's role outside the reproductive system. Animal and early human studies suggest LH receptors exist in the brain, and elevated postmenopausal LH may contribute to amyloid precursor protein processing — a potential link to Alzheimer's disease risk — but this hypothesis has not been confirmed in large human trials and Health Canada has not issued guidance on it. The optimal LH:FSH ratio threshold for diagnosing PCOS remains debated; many guidelines have moved away from using the ratio as a standalone criterion. Reference ranges for LH also vary meaningfully between assay platforms, which can complicate interpretation when patients switch laboratories. The clinical significance of mildly elevated or mildly suppressed LH in otherwise asymptomatic individuals is not well established.

FAQs

What is a normal LH level, and what does it mean if mine is high or low?

Normal LH varies considerably by sex, age, and menstrual cycle phase — for example, a mid-cycle surge of 22–105 IU/L is expected in ovulating females, while the same value would be abnormal in a male or a woman in the luteal phase. A persistently high LH (alongside high FSH) in a woman under 40 can indicate premature ovarian insufficiency, while a high LH in the context of irregular cycles and an LH:FSH ratio greater than 2:1 may suggest PCOS. Low LH in either sex points toward a hypothalamic or pituitary problem. Always interpret your result against the reference range on your specific lab report (LifeLabs and Dynacare each publish their own intervals) and discuss it with a clinician.

How is LH different from FSH, and why are both tested together?

LH and FSH are both glycoprotein gonadotropins produced by the same gonadotroph cells in the anterior pituitary, and they share an identical alpha subunit — only their beta subunits differ, giving each its distinct biological role. FSH drives follicle development and sperm maturation, while LH triggers ovulation and testosterone production. Because they are co-secreted and co-regulated, an abnormal ratio (such as LH:FSH greater than 2:1 in PCOS, or both elevated in primary gonadal failure) is often more informative than either value alone. Ordering them together, along with estradiol or testosterone, gives clinicians a complete picture of HPG axis function.

Can testosterone therapy affect my LH levels?

Yes — exogenous testosterone is one of the most common causes of suppressed LH in clinical practice. Testosterone feeds back negatively on both the hypothalamus and the pituitary, reducing GnRH pulsatility and shutting down LH secretion; in some men on testosterone replacement, LH falls to undetectable levels within weeks. This suppression also halts intratesticular testosterone production and can cause testicular atrophy and infertility. Men who want to preserve fertility while on testosterone therapy should discuss alternatives (such as clomiphene citrate or hCG co-administration) with a urologist or endocrinologist before starting treatment.

Is an LH blood test covered by provincial health insurance in Canada?

In most provinces, LH testing ordered by a physician is covered under provincial health insurance when there is a documented clinical indication — such as infertility investigation, menstrual irregularity, or suspected hypogonadism. Routine or self-requested LH testing without a physician's requisition is generally not covered and may cost $30–$80 out of pocket at private labs. Coverage rules differ by province; patients in Ontario, British Columbia, and Alberta should confirm with their provider whether the specific indication qualifies under their provincial schedule of benefits.

Does LH change during menopause, and does that matter for hormone therapy decisions?

Yes — as ovarian function declines, the negative feedback on the pituitary weakens, and LH (along with FSH) rises substantially; postmenopausal LH levels of 14–52 IU/L are typical, compared to 2–15 IU/L in the follicular phase. Clinicians sometimes use an elevated FSH (above 40 IU/L) combined with symptoms to confirm menopause, though LH alone is not a diagnostic criterion. Menopausal hormone therapy (MHT) suppresses elevated LH and FSH by restoring negative feedback, but the SOGC's 2021 menopause guidelines emphasize that the goal of MHT is symptom relief and risk reduction — not normalization of gonadotropin levels per se.

Sources

All glossary termsUpdated 2026-05-22