LH in Serum

Low LH usually suggests reduced hypothalamic or pituitary drive, especially when sex steroid levels are also low. Causes include hypothalamic-pituitary disorders, hyperprolactinemia, functional suppression from undernutrition, excessive exercise / low energy availability, severe stress or systemic illness, and suppressive medications or exogenous androgens. In men, low or inappropriately normal LH with low testosterone suggests secondary hypogonadism.

High LH usually reflects reduced gonadal feedback.

In men, it suggests primary testicular dysfunction when testosterone is low, and may indicate compensated / subclinical primary hypogonadism when testosterone is still normal. Causes include Klinefelter syndrome, orchitis, testicular injury, chemotherapy or radiation, and anorchia.

In women, LH must be interpreted in the context of cycle phase and menopausal status: it normally rises around ovulation and is commonly elevated after menopause. Persistently high LH outside the expected physiologic setting may be seen with reduced ovarian function, including primary ovarian insufficiency; PCOS may show relatively increased LH, but LH:FSH ratio is not a diagnostic criterion on its own.