If you have ever peed on an ovulation strip, you have measured LH. The surge that the strip is hunting for, lasting roughly 24 to 48 hours, is what makes the dominant follicle rupture and release an egg. The strip works because LH spikes five to ten times above baseline before ovulation, then falls.
Outside that surge, LH answers different questions. The most common one in real life is PCOS. Women with PCOS often have an LH/FSH ratio above 2 on day 3, the result of a hypothalamus pulsing GnRH too fast and skewing the gonadotropin balance. The Rotterdam criteria do not require it for diagnosis, but when the ratio is elevated alongside hyperandrogenism and irregular cycles, it lines up with the clinical picture. Note: in obese PCOS the ratio is often normal because insulin amplifies ovarian androgens through a different pathway.
LH also matters in male hypogonadism (high LH with low testosterone means the testis is the problem; low LH with low testosterone points at the pituitary), in menopause (chronically elevated), and in spotting exogenous testosterone use (suppressed LH with high testosterone is the textbook giveaway).
What LH measures
LH is released in pulses by the anterior pituitary in response to GnRH from the hypothalamus. The pulse pattern matters as much as the average level, fast pulses (one every 60–90 minutes) are characteristic of PCOS and skew gonadotropin output toward LH over FSH.
At the gonad:
- In women: LH stimulates ovarian theca cells to produce androgens (precursors for estradiol), and the LH surge triggers ovulation. After ovulation, LH supports the corpus luteum.
- In men: LH stimulates Leydig cells to make testosterone. LH is the brain's testosterone-production accelerator.
Like FSH, LH is feedback-regulated by sex steroids and inhibins. The system is highly sensitive, small changes in estradiol can produce large LH effects, especially the mid-cycle positive feedback that triggers the surge.
LH reference ranges
| Grupo demográfico | Bajo | Alto | Unidad |
|---|---|---|---|
| Women, follicular phase | 1.7 | 8.6 | mIU/mL |
| Women, mid-cycle surge | 21.9 | 56.6 | mIU/mL |
| Women, luteal phase | 0.6 | 14 | mIU/mL |
| Postmenopausal women | 14.2 | 52.3 | mIU/mL |
| Adult men | 1.7 | 8.6 | mIU/mL |
| Pre-pubertal children | 0 | 1 | mIU/mL |
| PCOS LH/FSH ratio cutoff | 2 | 5 | ratio |
Cycle- and age-dependent:
- Women, follicular phase: 1.7–8.6 mIU/mL.
- Women, mid-cycle surge: 21.9–56.6 mIU/mL, peaks for 24–48 hours, then falls.
- Women, luteal phase: 0.6–14 mIU/mL.
- Postmenopausal women: 14.2–52.3 mIU/mL.
- Adult men: 1.7–8.6 mIU/mL.
- Pre-pubertal children: below 1 mIU/mL.
The LH/FSH ratio is informative on day 3 (early follicular phase). Normal is approximately 1:1. A ratio above 2 (LH disproportionately elevated) is a classic finding in PCOS, though not all PCOS patients have it.
What high LH means
The differential for high LH:
- Menopause / premature ovarian insufficiency: both FSH and LH elevated; FSH usually higher than LH. The "menopausal pattern."
- Polycystic ovary syndrome: LH disproportionately high relative to FSH (LH/FSH ratio often >2). Reflects accelerated GnRH pulse frequency.
- Mid-cycle surge: physiologic and brief. Don't pathologize a high LH drawn at days 12–14 in a regularly cycling woman.
- Primary testicular failure: Klinefelter, post-chemotherapy, post-orchitis. LH and FSH both elevated, testosterone low.
- Androgen receptor insensitivity: rare; LH high despite normal/high testosterone.
- Pituitary gonadotropin-secreting adenoma: rare.
- Precocious puberty (central): pubertal LH levels in a young child.
What low LH means
Low LH points upstream, to hypothalamus or pituitary.
- Hypothalamic amenorrhea / functional hypogonadotropic hypogonadism: energy deficit, low BMI, overtraining, severe psychological stress. Both LH and FSH low; reversible.
- Hyperprolactinemia: elevated prolactin suppresses GnRH pulsatility.
- Pituitary disease: adenoma (compressive), infarction (Sheehan's), surgery, radiation.
- Anorexia nervosa: severe hypothalamic suppression.
- Kallmann syndrome: congenital GnRH deficiency, often with anosmia.
- Hemochromatosis: iron deposition in pituitary.
- Combined oral contraceptives, GnRH agonists/antagonists: physiologic suppression.
- Pregnancy: high estradiol and progesterone suppress LH.
- Exogenous testosterone or anabolic steroids: strong negative feedback. Suppressed LH with high testosterone is the classical pattern of exogenous use.
The LH surge and the LH/FSH ratio
Two LH patterns matter most clinically:
The ovulation surge. Estradiol rising above ~200 pg/mL for ~50 hours flips LH negative feedback to positive feedback. LH spikes 5–10x baseline for 24–48 hours, then falls. Ovulation occurs ~36 hours after surge onset, typically the day of or after peak. Home ovulation predictor kits detect urinary LH a day before ovulation.
For timed-intercourse fertility plans, OPKs are simple and reliable for women with regular cycles. Less reliable in PCOS (chronic mid-range LH gives false positives) and in older perimenopausal women (chronically elevated LH).
The LH/FSH ratio in PCOS. On day 3, FSH should slightly exceed LH (ratio ~0.8–1.0). In PCOS, accelerated GnRH pulses preferentially stimulate LH release, raising the ratio above 2 in 30–50% of PCOS patients. The Rotterdam criteria do not require an elevated ratio for diagnosis, but it is supportive when present. In obese PCOS, the ratio is often normal, high insulin amplifies ovarian androgen production through other pathways.
LH alone has limited utility in routine fertility evaluation; the patterns and pairings matter more than a single number.
Rastrea este biomarcador a lo largo del tiempo en AskAnything.health — sube tus resultados de laboratorio y ve las tendencias de un vistazo.
When to act on LH
- Day 3 LH/FSH ratio >2 with hyperandrogenism and irregular cycles: consistent with PCOS.
- High LH and FSH with low estradiol or testosterone: primary gonadal failure (menopause/POI in women, primary testicular failure in men). Workup as appropriate.
- Low LH and FSH with low estradiol or testosterone: central (hypothalamic-pituitary) hypogonadism. Check prolactin, TSH, energy availability, MRI if indicated.
- Suppressed LH with high testosterone in a man: exogenous androgen use.
- Pre-pubertal child with elevated LH and FSH: pediatric endocrinology evaluation for precocious puberty.
- Single high LH in a regularly cycling woman: could be the surge; not an automatic abnormality.
Esta información es solo con fines educativos y no sustituye el consejo médico profesional. Siempre consulta a tu proveedor de salud sobre tus resultados de laboratorio.
Tests that complete the picture
- FSH: paired with LH for ratio interpretation and primary vs. secondary localization.
- Estradiol: paired with LH for cycle staging and surge confirmation.
- Progesterone: confirms ovulation (mid-luteal).
- Testosterone: male hypogonadism workup; PCOS workup in women.
- Prolactin: common cause of low LH/FSH.
- DHEA-S: adrenal androgen contribution in PCOS.
- AMH: ovarian reserve.
- TSH: thyroid disease as a cause of menstrual irregularity.