Summary
Luteinising Hormone (LH) is released by the pituitary gland and, in women, surges mid-cycle to trigger ovulation. In men, it stimulates the testes to produce testosterone. LH is interpreted alongside FSH and the sex hormones to assess fertility, diagnose PCOS, identify the cause of low testosterone, and localise reproductive problems to the gonads or the pituitary.
In women, LH rises gradually through the follicular phase and then surges sharply about 24–36 hours before ovulation — the basis of ovulation predictor kits. In men, LH provides the constant signal that drives Leydig cell testosterone production.
The LH:FSH ratio is clinically useful: in PCOS, LH is often elevated relative to FSH (a raised LH:FSH ratio). In primary gonadal failure (ovarian or testicular), both LH and FSH rise. In pituitary or hypothalamic problems, both are low.
LH is therefore a key part of investigating irregular periods, infertility, low testosterone, and disorders of puberty.
What It Is
LH is a glycoprotein gonadotropin secreted by anterior pituitary gonadotrophs under pulsatile GnRH control. It shares the common alpha subunit of the glycoprotein hormones with a specific beta subunit.
In women, the mid-cycle LH surge — triggered by rising oestradiol via positive feedback — induces final oocyte maturation, follicle rupture (ovulation), and formation of the corpus luteum. In men, LH binds Leydig cell receptors to stimulate testosterone biosynthesis. Sex steroids exert negative feedback on LH secretion.
Reference ranges (women): follicular 2.4–12.6 IU/L; mid-cycle surge 14–96 IU/L; luteal 1–11.4 IU/L; postmenopausal 7.7–59 IU/L. Men: 1.7–8.6 IU/L.
Functions
Ovulation trigger
The mid-cycle LH surge triggers final egg maturation and ovulation — the central event of the fertile window.
Testosterone production
In men, LH stimulates the Leydig cells of the testes to produce testosterone.
PCOS assessment
An elevated LH:FSH ratio is a recognised feature of polycystic ovary syndrome.
Localising reproductive problems
Together with FSH, LH distinguishes gonadal failure (both high) from pituitary/hypothalamic causes (both low).
Reference Ranges
LH — Luteinising Hormone
Measured in IU/L| Status | Range (IU/L) | What it means |
|---|---|---|
| Low | < 2.4 | Low LH — suggests pituitary/hypothalamic suppression (secondary hypogonadism). |
| Normal (follicular) | 2.4–12.6 | Normal early-cycle range in women; normal range in men. |
| Mid-cycle surge | 14–96 | Ovulatory surge — triggers ovulation 24–36 hours later. |
| Elevated | > 25 (non-surge) | Persistently high — menopause, gonadal failure, or raised LH:FSH ratio in PCOS. |
Female ranges depend on cycle phase and menopausal status. The brief mid-cycle surge can confound a single reading. Interpret alongside FSH (and the LH:FSH ratio) and sex hormones.
Symptoms of Imbalance
LH abnormalities reflect disturbances in the reproductive axis; symptoms relate to the underlying cause.
- Irregular or absent periods
- Low libido
- Infertility
- Low testosterone symptoms in men (fatigue, reduced libido)
- Delayed puberty
- Symptoms of pituitary dysfunction
- Irregular periods (PCOS with raised LH:FSH ratio)
- Menopausal symptoms (hot flushes)
- Infertility
- Symptoms of primary gonadal failure
Causes of Imbalance
- Hypothalamic dysfunction (stress, low body weight, over-exercise)
- Pituitary disease or tumour
- Hyperprolactinaemia
- Kallmann syndrome
- Anabolic steroid use
- Menopause and ovarian failure
- Primary testicular failure (men)
- PCOS (raised LH:FSH ratio)
- Turner or Klinefelter syndrome
- Premature ovarian insufficiency
FAQs
The LH surge is a sharp, brief rise in LH that occurs in the middle of the menstrual cycle, triggered by peak oestradiol. It causes the mature follicle to release its egg about 24–36 hours later. Home ovulation predictor kits detect this surge in urine to identify the most fertile days. In a blood test, catching the surge depends on precise timing within the cycle.
An elevated ratio of LH to FSH (often around 2:1 or higher) in the early follicular phase is a recognised feature of polycystic ovary syndrome (PCOS). It reflects altered pituitary signalling in PCOS. However, the ratio is only one supporting feature — PCOS is diagnosed using a combination of irregular cycles, signs of androgen excess, and ultrasound findings, not the LH:FSH ratio alone.
In men, LH stimulates the testes to make testosterone. Measuring LH alongside testosterone identifies the cause of low testosterone: a low LH with low testosterone points to a pituitary or hypothalamic problem (secondary hypogonadism), whereas a high LH with low testosterone indicates the testes themselves are failing (primary hypogonadism). This distinction guides further investigation and treatment.
Yes. Physical and psychological stress, very low body weight, and excessive exercise can suppress the hypothalamic GnRH pulses that drive LH secretion. This lowers LH (and FSH), reducing sex hormone production and disrupting or stopping periods — a pattern known as functional hypothalamic amenorrhoea. Addressing the underlying stress, nutrition, and energy balance usually restores normal LH signalling.
References
- Hall JE. Neuroendocrine control of the menstrual cycle. In: Yen & Jaffe's Reproductive Endocrinology. 8th ed. Elsevier; 2019.
- Teede HJ, et al. International evidence-based guideline for the assessment and management of polycystic ovary syndrome. Hum Reprod. 2018;33(9):1602–1618. View source
- 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. View source