Unit Converter
Luteinizing hormone (LH)
(Pituitary Gonadotropin – Key Marker for Puberty, Ovulation, Infertility & Hypogonadism)
Synonyms
- LH
- Luteinizing hormone
- Interstitial cell–stimulating hormone
- Pituitary gonadotropin
- Gonadotropin LH
Units of Measurement
- mIU/mL
- IU/L
Unit Conversions
1 mIU/mL = 1 IU/L
(Direct 1:1 conversion)
LH is reported only in activity units, not mass or molar units.
Description
Luteinizing hormone (LH) is a glycoprotein hormone secreted by the anterior pituitary gland under the control of GnRH.
Functions:
- Regulates ovulation in females
- Stimulates testosterone production in males
- Drives puberty initiation
- Essential in menstrual cycle physiology
LH acts on:
- Theca cells in ovaries → androgen production
- Leydig cells in testes → testosterone secretion
Physiological Role
Females
- LH surge triggers ovulation
- Supports formation & maintenance of corpus luteum
- Regulates progesterone production
Males
- LH stimulates Leydig cells → testosterone
- Supports spermatogenesis indirectly
Puberty
- Rising LH levels are a hallmark of pubertal onset.
- Pediatric LH cutoffs help diagnose precocious puberty or delayed puberty.
Clinical Significance
HIGH LH
Females
- Primary ovarian failure (↑ LH + ↑ FSH, low estradiol)
- Turner syndrome
- Premature ovarian insufficiency
- Chemotherapy/radiation-associated gonadal failure
- Turner syndrome
- Polycystic Ovary Syndrome (PCOS)
- LH:FSH ratio often elevated (>2:1)
- LH:FSH ratio often elevated (>2:1)
- Perimenopause / Menopause
- LH markedly elevated
- LH markedly elevated
- Ovulation
- LH surge is diagnostic marker
- LH surge is diagnostic marker
- Gonadotropin-secreting pituitary adenoma (rare)
Males
- Primary testicular failure
- Klinefelter syndrome
- Orchitis
- Testicular trauma
- Klinefelter syndrome
- Low testosterone with high LH → primary hypogonadism
Children
- Central Precocious Puberty (CPP)
- Basal LH ≥ 0.3–0.7 IU/L (assay dependent)
- Post-GnRH stimulation LH ≥ 5–8 IU/L confirms CPP
- Basal LH ≥ 0.3–0.7 IU/L (assay dependent)
LOW LH
Pituitary/Hypothalamic Causes
- Hypopituitarism
- Functional hypothalamic amenorrhea
- Hyperprolactinemia
- Pituitary tumors
- Kallmann syndrome
- Chronic systemic illness
PCOS
LH may be upper normal, not low.
High estrogen/testosterone feedback
E.g., steroid abuse.
Obesity in adolescents
Blunts LH pulsatility.
Reference Intervals
(Tietz 8E + Endocrine Society + Mayo + ARUP)
Values vary by assay; ranges below are widely accepted clinical norms.
FEMALES
| Phase | LH (IU/L) |
| Follicular | 1.9 – 12.5 |
| Mid-cycle peak | 8.7 – 76.3 |
| Luteal | 0.5 – 16.9 |
| Post-menopause | 15 – 62 |
MALES
- 1.24 – 7.8 IU/L
CHILDREN
(Before puberty LH is very low)
- Prepubertal (Tanner I): <0.3–0.7 IU/L
- Pubertal onset (Tanner II+): >0.3–2 IU/L
- GnRH-stimulated LH: ≥5–8 IU/L suggests true puberty
Diagnostic Uses
1. Infertility Workup
Combines with:
- FSH
- Estradiol
- Testosterone
- AMH (ovarian reserve)
2. PCOS Evaluation
Elevated LH or LH:FSH ratio.
3. Puberty Disorders
- Precocious puberty
- Delayed puberty
4. Menopause Diagnosis
Persistently high LH + high FSH.
5. Gonadal Failure
Primary testicular / ovarian failure → high LH.
6. Hypogonadotropic Hypogonadism
Low LH + low sex steroids.
7. Monitoring Ovulation Induction
LH surge timing for:
- IUI
- IVF cycles
Analytical Notes
- Serum sample preferred
- Measure at consistent time (LH is pulsatile)
- Pediatric values highly assay-dependent
- Avoid during acute illness (temporarily suppressed)
- Interpreting LH always requires FSH + sex steroid levels
Clinical Pearls
- LH surge precedes ovulation by ~36 hours.
- High LH + high FSH = primary gonadal failure.
- Low LH + low FSH = central hypogonadism.
- Obesity suppresses LH pulsatility in adolescent girls.
- In PCOS, LH is often high even if FSH normal.
Interesting Fact
LH, FSH, TSH, and hCG all belong to the same glycoprotein hormone family, sharing a common α-subunit but having distinct β-subunits that determine biological specificity.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hormones & Reproductive Endocrinology
- Endocrine Society Guidelines - Hypogonadism, PCOS, Menopause
- Mayo Clinic Laboratories - LH
- ARUP Consult - Gonadotropin Testing
- MedlinePlus / NIH - Luteinizing Hormone