What it measures.
Luteinizing Hormone (LH) is a pituitary glycoprotein that triggers ovulation in women and stimulates testosterone production in men. A sharp mid-cycle LH surge (20-80 mIU/mL) triggers oocyte maturation and follicle rupture — the signal that ovulation prediction kits detect. The LH:FSH ratio is elevated to 2:1 or greater in approximately 40-60% of women with PCOS. In men, LH level is critical for distinguishing primary from secondary hypogonadism.
LH released by the anterior pituitary in GnRH-driven pulses. In women, the mid-cycle estradiol surge triggers the LH surge, causing ovulation 35-44 hours later. In men, LH stimulates Leydig cells to synthesize testosterone.
Why it matters.
LH is the biological ovulation trigger — understanding your LH pattern is essential for timing intercourse or IUI. The LH:FSH ratio helps diagnose PCOS. In men, the LH level determines whether low testosterone is from testicular failure (high LH) or pituitary dysfunction (low LH) — which determines treatment.
Physiology.
LH acts on theca cells in ovarian follicles to produce androgens (which granulosa cells convert to estrogen). The LH surge triggers the dominant follicle to complete meiosis and ovulate. In the luteal phase, LH supports the corpus luteum's progesterone production. In men, LH stimulates Leydig cells to produce testosterone via cAMP signalling.
Testing & preparation.
How to prepare
- Women: Day 2-5 for baseline LH:FSH ratio
- Mid-cycle LH measured via OPK (urine) or serum if timing ovulation
- Men: no timing constraints
- Morning draw preferred
When to test
Women: Day 3 for PCOS evaluation; mid-cycle for ovulation timing. Men: when testosterone is low to classify hypogonadism type.
How often
As needed per clinical context. Not a routine monitoring marker.
Interpretation.
High luteinizing hormone
Common causes:
- Mid-cycle LH surge (normal ovulation — 20-80+ mIU/mL)
- PCOS (tonically elevated LH with LH:FSH >2:1)
- Primary gonadal failure (elevated LH + elevated FSH)
- Menopause (persistently elevated LH and FSH)
- Primary testicular failure in men
Implications:
- PCOS: chronically elevated LH drives ovarian androgen excess
- LH:FSH >2:1 with anovulation and hyperandrogenism supports PCOS diagnosis
- Paradoxical finding: in PCOS, elevated LH:FSH worsens ovulation but improves live birth after ovulation induction
- Men: elevated LH with low testosterone = primary hypogonadism (testes not responding)
Low luteinizing hormone
Common causes:
- Hypothalamic amenorrhoea (stress, low BMI, excessive exercise)
- Hyperprolactinaemia (prolactin suppresses GnRH pulses)
- Pituitary disorders
- Exogenous testosterone or anabolic steroids (men)
- Kallmann syndrome (congenital GnRH deficiency)
Implications:
- Low LH + low testosterone = secondary hypogonadism (treatable with gonadotropins)
- Low LH + low FSH + low estradiol + normal AMH = hypothalamic amenorrhoea
- Investigate pituitary function and prolactin
Optimization.
Diet
- No specific foods modulate LH directly
- Adequate caloric intake restores LH pulsatility in hypothalamic amenorrhoea
- Inositol (myo-inositol + D-chiro-inositol) may improve LH:FSH ratio in PCOS
Lifestyle
- Stress reduction and adequate sleep support GnRH pulsatility
- Weight restoration for underweight amenorrhoea
- Weight loss in PCOS can normalise LH:FSH ratio
Supplements
- Myo-inositol (4g/day) + D-chiro-inositol (100mg/day) studied in PCOS
- No supplements reliably raise low LH in secondary hypogonadism
FAQs.
What does the LH:FSH ratio tell you?
A ratio >2:1 on Day 3 is a classic PCOS indicator, reflecting disproportionate LH drive that causes excess ovarian androgen production. However, this ratio is not required for PCOS diagnosis — the 2023 guideline uses Rotterdam criteria (oligo-anovulation, hyperandrogenism, and/or polycystic morphology).
How do ovulation predictor kits work?
OPKs detect the LH surge in urine. When serum LH exceeds approximately 15-20 mIU/mL, the kits turn positive. Ovulation typically follows 35-44 hours after the LH surge begins. Testing daily from around Day 10 captures the surge in most women.
Can LH be too high even outside the surge?
Yes. Tonically elevated LH (outside mid-cycle) is a hallmark of PCOS. It drives excess androgen production from the ovaries, contributing to acne, hirsutism, and anovulation. In men, chronically elevated LH with low testosterone indicates the testes aren't responding to stimulation.