LH triggers ovulation in women and commands testosterone production in men. Its mid-cycle surge is the target of ovulation predictor kits, and its ratio to FSH once defined, and now only supports, the diagnosis of PCOS.
Standard range versus optimal range
| Framework | LH value | Source |
|---|---|---|
| Women, follicular phase | about 2-8 IU/L | Common laboratory range |
| Ovulation surge | above 25 IU/L, brief peak | Reproductive endocrinology |
| Postmenopause | typically above 15-30 IU/L | STRAW+10 staging |
| Adult men | about 1.7-8.6 IU/L | Common laboratory range |
When it runs high
High LH outside the ovulatory surge reflects gonadal failure with the pituitary compensating, or the unbalanced secretion pattern of PCOS, where an LH to FSH ratio above two or three was historically used as supporting evidence.
- Menopause and primary gonadal failure
- Polycystic ovary syndrome, with characteristic pulse pattern
- The normal ovulatory surge
- Pituitary adenomas producing gonadotropins, rare
When it runs low
Low LH with low sex steroids means the pituitary is not sending the production signal, directing the workup to the brain. In athletes and in low energy availability the axis quiets down as an energy-saving measure.
- Hypothalamic amenorrhea from stress, low weight or overtraining
- Pituitary disease
- Hyperprolactinemia suppressing the axis
- Opioids and anabolic steroid use
The trigger and the foreman
LH does two jobs with one pulse train. In women a massive mid-cycle surge ruptures the mature follicle and releases the egg, the event every ovulation kit detects in urine. In men the same hormone pulses hourly into the testes and orders the Leydig cells to make testosterone. When the testes cannot answer, LH rises, which is how a simple blood test separates testicular from pituitary causes of low testosterone.
The PCOS connection
In polycystic ovary syndrome the rapid pulse frequency of the hypothalamus favors LH over FSH, and an elevated LH to FSH ratio became a classic teaching point. Modern diagnostic criteria under the Endocrine Society and international guidelines no longer require it, because many women with PCOS have a normal ratio, but a high LH still supports the diagnosis and explains the anovulation at its core. The practical message is that a normal LH never rules PCOS out.
Reading it as a pair
LH alone rarely answers a question, because its meaning depends entirely on the FSH and sex steroid measured beside it. High LH and FSH together means the gonads failed, low LH and FSH together means the pituitary went quiet, and a lone LH spike on cycle day fourteen means ovulation is hours away. Draw it with its partners, timed to the cycle, and the axis explains itself.
Related calculators
Related biomarkers FSH · Total testosterone · Prolactin