Luteinizing Hormone (LH) Test: Normal Range, High and Low

What the LH test shows

Luteinizing hormone (LH) is not made by the ovaries or testicles. The pituitary gland releases it in pulses, on orders from the hypothalamus, to tell the gonads what to do — so it anchors the reproductive hormone work-up, as MedlinePlus explains.

What LH does depends on sex. In women, a sharp mid-cycle LH surge triggers ovulation and forms the corpus luteum that makes progesterone — the surge home ovulation kits detect in urine, per StatPearls. In men, LH drives the testicles’ Leydig cells to make testosterone.

LH is almost always measured with FSH, the other pituitary gonadotropin. Together they localize a problem: high LH and FSH mean the gonads are failing — the pituitary is shouting and getting no answer — while low or inappropriately normal values point to the pituitary or hypothalamus above them.

LH normal range

LH is reported in mIU/mL, numerically identical to the SI unit IU/L (1 mIU/mL = 1 IU/L), so US and international reports use the same numbers. In women the level swings across the menstrual cycle, so the phase matters as much as the value:

The mid-cycle figure is a brief spike, not a resting level, so baselines are drawn early (days 2–5). Ranges depend on the lab, assay, sex, age and — in women — the cycle day, so read yours against your own report.

Why LH is high

A high LH usually means the gonads are not responding, so the pituitary turns the signal up. By frequency:

• Menopause — by far the commonest. As the ovaries wind down, estrogen falls, its feedback brake is lost, and LH and FSH rise and stay high, as StatPearls notes — expected, not disease.
• Primary ovarian insufficiency (POI) — the same high LH and FSH with low estradiol, but before age 40 with absent or irregular periods — Turner syndrome, the Fragile X premutation, autoimmune disease, cancer treatment.
• Primary testicular failure (men) — high LH with low testosterone points to the testicles, not the pituitary (Klinefelter syndrome, mumps orchitis, injury or chemo). The Endocrine Society advises LH and FSH to separate this from a pituitary cause.
• PCOS — LH is often mildly raised, sometimes out of proportion to FSH — variable, and not used alone to diagnose it.
• Central precocious puberty — LH rising early in a young child; rarely, a gonadotropin-secreting pituitary tumour.

High LH is rarely an emergency — it flags a state such as menopause or gonadal failure to confirm and manage. But early puberty in a young child needs prompt evaluation.

Why LH is low

A low — or inappropriately normal — LH beside low sex hormones points above the gonads, to the pituitary or hypothalamus: secondary (hypogonadotropic) hypogonadism. Several causes are reversible:

• Functional hypothalamic suppression — low body weight, disordered eating, heavy endurance training or major stress switch off the GnRH pulses that drive LH; a leading cause of lost periods in young women and low testosterone in lean, hard-training men.
• Exogenous hormones and drugs — testosterone or anabolic-steroid use shuts LH down (a common, often unspoken cause in men), as do opioids and high-dose steroids; the combined pill suppresses LH by design.
• High prolactin — a prolactinoma, some medications or an underactive thyroid raise prolactin, which suppresses LH — a treatable cause worth excluding.
• Pituitary or hypothalamic disease — an adenoma, Sheehan syndrome, surgery or radiation, or congenital GnRH deficiency (Kallmann syndrome, with reduced smell), knocking out gonadotropins, sometimes as absent or delayed puberty.

Low LH with low sex hormones plus headaches or visual changes suggests a pituitary mass; the Endocrine Society advises MRI when secondary hypogonadism is severe or prolactin is high.

What to test alongside

LH is read as a pattern, never alone:

• FSH — the inseparable partner that localizes the problem.
• Estradiol (women) with testosterone and free testosterone (men) — the sex hormones LH is read against: low beside high LH means gonadal failure; low beside low or normal LH, a pituitary cause.
• Progesterone — confirms ovulation followed the surge.
• Prolactin — high prolactin suppresses LH, a common reversible cause of low values.
• AMH, 17-OH-progesterone, DHEAS and SHBG — ovarian reserve plus the androgen-excess work-up in PCOS-type pictures.
• hCG — rules out pregnancy behind absent periods; mimics LH structurally.
• TSH and free T4 — thyroid disease disturbs cycles and can raise prolactin.

What to do about an abnormal result

1. Don’t self-treat. Don’t start testosterone, “hormone boosters” or supplements to move a number — testosterone and anabolic use suppress LH and harm fertility.
2. Mind the timing. In menstruating women LH tracks the cycle day — a mid-cycle surge is normal — so an isolated high value is often just ovulation; repeat around days 2–5. High-dose biotin distorts the assay, so stop it two days before.
3. Read the pattern. LH is interpreted with FSH plus estradiol (women) or testosterone (men): high beside low sex hormones points to the gonads, low or normal to the pituitary/hypothalamus (where prolactin and MRI come in).
4. Who to see. Start with your primary-care doctor or GP, who runs the amenorrhoea or low-testosterone work-up and refers to an endocrinologist, gynecologist or fertility specialist as needed.

Mini-FAQ

What does a high LH level mean?

In women, usually menopause — or, before age 40, primary ovarian insufficiency; in men, failing testicles (primary hypogonadism). High LH means the pituitary is working hard because the gonads are not responding.

What does a low LH level mean?

Low or inappropriately normal LH with low sex hormones points to the hypothalamus or pituitary, not the gonads — from stress, very low body weight, intense exercise, high prolactin, anabolic-steroid use or a pituitary problem. This is secondary (hypogonadotropic) hypogonadism.

Why are LH and FSH almost always tested together?

Both are pituitary gonadotropins whose pattern says more than either alone: high LH and FSH point to the gonads, low or normal values to the pituitary or hypothalamus, and the LH-to-FSH balance adds context in PCOS.

Does LH confirm ovulation or menopause?

An LH surge mid-cycle triggers ovulation — the signal home ovulation kits detect in urine. Persistently high LH and FSH with low estradiol and no periods fit menopause, though menopause is diagnosed clinically, not by one blood test.

When in the cycle should LH be measured?

For a baseline it is usually drawn early in the cycle, around days 2–5, when levels are stable. Timing matters because LH peaks sharply at mid-cycle, so a random high value may just be the ovulatory surge, not a problem.