Luteinizing Hormone
LH
Clinical Overview
LH is a gonadotropin hormone secreted by the anterior pituitary. In women, the LH surge triggers ovulation approximately 36–40 hours after the surge begins and stimulates progesterone production by the corpus luteum. In men, LH stimulates Leydig cells to produce testosterone. LH is a key fertility and menstrual cycle marker.
Why This Test Matters
The LH:FSH ratio is important in PCOS diagnosis — a ratio ≥2–3:1 on cycle day 3 supports PCOS. Urine LH surge detection kits predict ovulation for timed intercourse. An elevated LH with low testosterone in men indicates primary hypogonadism (testicular failure). Low LH with low testosterone suggests secondary (hypogonadotropic) hypogonadism.
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Female | 2.4 – 12.6 | mIU/mL | Follicular phase |
| Adults (18–64) | Female | 14 – 95.6 | mIU/mL | LH surge (ovulation) |
| Adults (18–64) | Male | 1.7 – 8.6 | mIU/mL | — |
Also reported in: IU/L.
What Causes Abnormal Results?
High LH Causes
- LH surge (normal — signals ovulation)
- Menopause or premature ovarian insufficiency
- Primary hypogonadism in men (testicular failure)
- PCOS (elevated LH with high LH:FSH ratio)
- Polycystic ovary syndrome
Low LH Causes
- Hypogonadotropic hypogonadism (pituitary or hypothalamic failure)
- Hyperprolactinemia
- Eating disorders and excessive exercise
- Oral contraceptive use
Signs & Symptoms to Watch For
How to Prepare for This Test
In women, the timing of measurement within the menstrual cycle is critical. For fertility evaluation, draw on cycle day 2–3. For detecting the LH surge, measure daily from cycle day 10–14. No fasting required.
Factors That Can Affect Results
- Cycle day (LH peaks dramatically during ovulation)
- Oral contraceptives (suppress LH)
- Pulsatile secretion pattern (a single measurement may miss the LH surge)
Related Topics
Frequently Asked Questions
How is the LH:FSH ratio used to diagnose PCOS?
In polycystic ovary syndrome, the pituitary releases pulses of LH more frequently and at higher amplitude than normal. A day 3 LH:FSH ratio above 2:1 or 3:1 is found in approximately 40–60% of women with PCOS. However, a normal ratio does not exclude PCOS — diagnosis requires the full Rotterdam criteria (two of three: irregular ovulation, clinical/biochemical hyperandrogenism, polycystic ovaries on ultrasound).