Luteinizing Hormone (LH): What It Does and What Your Level Means

The short answer

Luteinizing hormone (LH) is made by the anterior pituitary gland at the base of the brain and released in pulses, under the command of gonadotropin-releasing hormone (GnRH) from the hypothalamus. In the menstrual cycle, its defining act is the mid-cycle LH surge: a brief, steep rise that causes the dominant ovarian follicle to rupture and release an egg roughly 24–36 hours later. That surge is what an ovulation predictor kit picks up in urine.

The single most useful structural fact about LH is this: it is not a steady background level. It is low for most of the cycle, spikes for about a day and a half, then falls. So a number on a lab report tells you almost nothing unless you know which cycle day the blood was drawn — and unless you read it against that lab's reference range, because ranges vary between laboratories and assays.

What LH actually does, tissue by tissue

LH is a glycoprotein hormone that acts on the LH/choriogonadotropin receptor (LHCGR), a G-protein-coupled receptor sitting on specific ovarian cells. Where it lands determines what it does.

• Theca cells (the outer layer of a growing follicle) carry LH receptors from early on. LH tells them to convert cholesterol into androgens, mainly androstenedione and testosterone.
• Granulosa cells (the inner layer) respond to FSH, not LH, in the first half of the cycle. FSH switches on the enzyme aromatase, which converts those theca-made androgens into oestradiol. This is the two-cell, two-gonadotropin model: LH supplies the raw material, FSH supplies the factory.
• The corpus luteum. After ovulation, the collapsed follicle reorganises into the corpus luteum, whose cells are stuffed with LH receptors. LH keeps it alive and keeps it producing progesterone, the hormone that stabilises the uterine lining in the second half of the cycle. When LH support fades and no pregnancy occurs, the corpus luteum involutes, progesterone falls, and the lining is shed.

LH across a whole life, not just an ovulation test

Most articles treat LH as a fertility gadget. It is a hormone with a job at every life stage, and knowing the arc makes any single result easier to place.

• Childhood. LH is very low. The hypothalamus is deliberately quiet, so the pituitary has nothing to say.
• Puberty. It begins when GnRH starts pulsing again, first at night. LH pulses follow, the ovary wakes, oestradiol rises. Unusually early or conspicuously absent LH in a child is a paediatric endocrine question, not a home-test one.
• Reproductive years. A low baseline, one surge per ovulatory cycle, then suppression again through the luteal phase.
• Pregnancy. LH is suppressed, and human chorionic gonadotropin (hCG) takes over the same receptor — which is how hCG sustains the corpus luteum in early pregnancy, and why hCG can cross-react with some ovulation strips and produce a "positive" that has nothing to do with ovulation.
• Perimenopause and after. LH becomes erratic, then permanently high. More on that below, because it is where the money gets wasted.

LH is not a female-only hormone either. In men it acts on testicular Leydig cells to drive testosterone production, and low LH with low testosterone points to the same hypothalamic and pituitary problems it does in women.

The surge: a feedback flip worth understanding

Most of the time, oestrogen suppresses LH. Rising oestradiol tells the hypothalamus and pituitary to ease off — classic negative feedback, the same loop a thermostat uses. This is why LH stays low through the follicular phase even as oestradiol climbs.

Then something genuinely unusual happens. If oestradiol stays high enough for long enough — sustained levels over roughly 36–48 hours, produced by a single dominant follicle that has out-competed the rest — the sign of the feedback flips. The same oestradiol that was suppressing LH now stimulates it. That is positive feedback, and it is rare in human physiology precisely because it is explosive: more oestrogen drives more LH, which drives more oestrogen. The pituitary dumps its stored LH, producing a spike several times higher than baseline.

The surge then does three things at once inside the follicle: it restarts the egg's stalled meiotic division, it triggers enzymes that digest the follicle wall so the egg can escape, and it reprograms the granulosa cells to start making progesterone (luteinisation). Ovulation follows about 24–36 hours after the surge begins, usually around 10–12 hours after the LH peak itself.

The practical version: the surge is the signal, not the event. A positive ovulation test means your body has issued the order, not that the egg is out. And a surge does not guarantee an egg was actually released — follicles can luteinise without rupturing. If confirming ovulation matters clinically, a mid-luteal progesterone level (drawn about seven days before the expected period) is the better check, and it is one to arrange with a clinician rather than a strip. Our guide to the menstrual cycle phases and the menstrual cycle explorer show where LH sits relative to FSH, oestradiol and progesterone across a full cycle; how long ovulation lasts covers the fertile window itself.

LH reference ranges, and why the number alone is useless

The figures below are typical adult serum LH ranges, in international units per litre (IU/L). Ranges vary meaningfully between laboratories and assay platforms, and they vary by cycle day. Always read your result against the range printed on your own report, next to the date the blood was taken — not against a number you found online.

Notice the overlap. A result of 10 IU/L is unremarkable on day 5, an early surge on day 12, and slightly odd on day 22. This is the core reason a mail-order "hormone panel" that reports LH without a cycle day is selling you a number, not information. If you are trying to make sense of a report you already have, our lab results explainer puts values in context, and at-home hormone tests vs. a doctor's test covers what these panels can and cannot tell you.

What high LH means

1. The normal surge

The commonest cause of a high LH in a menstruating woman is that the blood was drawn during her surge. That is not a finding; it is a coincidence of timing. It is also the first thing a clinician will try to rule out, by asking the question you should be able to answer before you test at all: what cycle day is it?

2. PCOS

In polycystic ovary syndrome, GnRH pulses run fast, and fast pulses preferentially favour LH secretion over FSH. The result is a raised LH:FSH ratio, classically quoted as greater than 2:1, with LH persistently elevated rather than surging and falling. High LH drives theca cells hard, which raises androgens, which is part of why PCOS produces acne, unwanted hair growth and irregular or absent ovulation.

Two honest caveats. First, the LH:FSH ratio is a classic finding, not a diagnostic one: it is not part of the Rotterdam criteria used in the current international PCOS guideline, and a substantial share of women with PCOS have a perfectly normal ratio. Diagnosis rests on a combination of irregular ovulation, clinical or biochemical hyperandrogenism, and ovarian appearance on ultrasound (or a raised anti-Müllerian hormone), with other causes excluded. Second, and this is the practical one: persistently elevated LH in PCOS can produce false-positive ovulation predictor kit results, because the strip cannot tell a real surge from a chronically high baseline. Women with PCOS may see "positive" strips repeatedly in a cycle in which no egg was ever released. See PCOS symptoms, the full PCOS guide and our PCOS hub.

3. Primary ovarian insufficiency

If the ovaries stop responding before age 40, the pituitary shouts louder: LH and FSH rise while oestradiol falls. Persistently raised gonadotropins with irregular or absent periods under 40 is a picture that needs a clinician, not a home test — it carries implications for bone density, cardiovascular risk and fertility. AMH and ovarian reserve is a related but different measurement, and it does not diagnose menopause either.

4. Menopause

Here is the mechanism people are rarely given. The ovary's follicles are the source of oestradiol and of inhibin B, and together those two hormones are what hold FSH and LH down. As the follicle pool is exhausted, that brake is removed. FSH rises first and highest, because inhibin B falls early, and LH follows. After menopause, LH sits several times higher than a typical follicular-phase value — not because anything is broken in the pituitary, but because it is calling out to an ovary that is no longer answering.

What low LH means

Low LH, especially low LH together with low FSH and low oestradiol, points upstream to the hypothalamus or pituitary. This is called hypogonadotropic hypogonadism, and the pattern is diagnostically useful: the ovary is fine; the signal never arrived.

• Functional hypothalamic amenorrhoea (low energy availability). This is the common one, and the commonly missed one. When energy intake does not cover energy expenditure — through under-eating, high training volume, illness or psychological stress, alone or in combination — the hypothalamus slows its GnRH pulses. LH falls, follicles stall, oestradiol drops, periods become irregular and then stop. The Endocrine Society's clinical practice guideline treats this as a diagnosis of exclusion in women whose periods have been absent for three or more months, and it is explicit that the fix is correcting the energy deficit — more fuel, less training load, psychological support where relevant — rather than layering hormones on top of an unaddressed cause. Body weight can look entirely "normal": you do not have to be visibly underweight to be under-fuelled. The stakes are not just missed periods, because sustained low oestradiol costs bone. See exercise and bone density and managing stress.
• Pituitary problems. A prolactin-secreting adenoma, other pituitary tumours, surgery, radiotherapy, head injury or infiltrative disease can all blunt LH output. Raised prolactin in particular suppresses GnRH pulses directly, which is why prolactin is usually checked alongside LH and FSH.
• Hormonal contraception. Combined pills work partly by flattening LH: steady exogenous oestrogen and progestogen hold the feedback loop down, so no surge occurs and no ovulation occurs. A low LH on the pill is the medication doing its job, not a disorder. It also means an LH result taken while on hormonal contraception cannot tell you anything about your underlying cycle — something worth knowing before you pay for a panel. Any decision about your contraception belongs with your clinician, not with a test strip.

The midlife problem: why one LH test cannot diagnose perimenopause

This is the part most articles skip, and it is where a lot of money gets wasted.

Perimenopause is not a smooth decline. As the follicle pool thins, cycles become erratic: some months a follicle recruits early and oestradiol spikes higher than it ever did in your twenties; other months nothing much happens at all. FSH and LH follow that chaos. A woman can have a postmenopausal-looking FSH and LH in one cycle and an entirely premenopausal-looking result six weeks later, in the same body, with the same symptoms. This is not lab error. It is the physiology of a system whose feedback signal has become intermittent.

Which is why the guidelines are blunt about it. NICE's menopause guideline advises diagnosing perimenopause and menopause in women over 45 on symptoms and menstrual pattern alone, without laboratory tests. FSH testing is reserved for narrower situations: for example women aged 40–45 with menopausal symptoms and a change in their cycle, or women under 40 in whom primary ovarian insufficiency is suspected. LH is not the recommended test even then. FSH is the one used, and it carries the same caveat about swinging between cycles.

Say it plainly: if you are over 45 with hot flushes, disturbed sleep and cycles that have gone haywire, a direct-to-consumer "hormone panel" measuring LH, FSH and oestradiol will most likely hand you a number that changes nothing about your management — and may falsely reassure you if it happens to land on a normal-looking day. That money is better spent on a consultation. We go through this in detail in menopause hormone testing, at-home menopause tests and how to compare at-home hormone tests.

Two consequences of erratic midlife LH are worth naming. First, ovulation predictor kits become unreliable in perimenopause, because the baseline LH is drifting upward: you can get positive strips in cycles where no egg is released. Second, unpredictable ovulation is exactly why pregnancy is still possible in perimenopause. UK guidance advises continuing contraception until 12 months after the final period if that period came at age 50 or over, or 24 months if it came before 50 — and which method suits you is a discussion for your clinician. Fertility-awareness methods based on mucus or temperature are not a reliable substitute for contraception: with typical use, roughly 2 to 23 women in 100 become pregnant within a year, depending on the method and how consistently it is used, and these methods are least reliable when cycles are irregular, which is precisely what perimenopause does to them. See perimenopause symptoms, irregular periods in perimenopause, perimenopause vs menopause and can you get pregnant after menopause.

LH and the symptoms you actually feel

LH itself is not what makes you feel anything. It is a signal to the ovary; what you feel comes from what the ovary does in response, which means oestradiol and progesterone. The cyclical misery some women get in the days before a period (aches, chills, fatigue, gut upset — the cluster people call period flu), along with period fatigue and period pain, tracks the luteal-phase progesterone-and-oestrogen withdrawal that follows LH's work, not LH levels themselves. The same logic applies to premenstrual mood symptoms, including PMDD: the evidence points to an abnormal sensitivity to normal hormonal change rather than to abnormal hormone levels, which is exactly why measuring LH will not explain them. Our hormone anatomy tool maps which hormone acts on which tissue.

One more piece of honesty. Claims that you should "cycle-sync" your diet or training to LH, and the idea that a mildly short luteal phase is a definable "luteal phase defect" requiring treatment, both run well ahead of the evidence. The supporting research is thin and contested, and neither is a settled clinical entity. Treat them as hypotheses, not facts, and be sceptical of anything sold on the strength of them.

When to see a doctor

See a clinician rather than self-managing from a home test kit if any of these apply.

• Your periods have stopped for three months or more and you are not pregnant, not using a method that stops periods, and not past menopause. Absent periods with a low-oestrogen state cost bone density, and time matters.
• You are under 40 and your periods have become irregular or stopped. This needs assessment for primary ovarian insufficiency, which has long-term bone and cardiovascular implications.
• You train hard or eat restrictively and your periods have become light, irregular or absent. This is the under-fuelled picture. It is treatable, and it is frequently mistaken for "just being fit".
• Irregular cycles with acne, hair growth on the face or body, or scalp hair thinning. A PCOS assessment is warranted, and it needs more than an LH:FSH ratio.
• Any bleeding after menopause (12 or more months without a period), or heavy or unpredictable bleeding in perimenopause. This always needs evaluation. See postmenopausal bleeding.
• Headaches, vision changes, unexplained milky nipple discharge, or profound fatigue alongside a low LH. These can point to a pituitary problem and should be assessed promptly.
• You have been trying to conceive for 12 months, or six months if you are 35 or over, without success — or your cycles are consistently shorter than 21 days or longer than 35 days. Both warrant a proper assessment rather than more strips.
• You have a lab result you cannot interpret and cannot date. Take it to a clinician along with the date of the test and, if you know it, the first day of your last period. Without the cycle day, the number cannot be read — by anyone.

This guide explains physiology and how tests are interpreted. It is not medical advice and it is not a diagnosis. Do not start, stop or change any medication or contraceptive on the strength of a hormone number: that decision belongs to you and your clinician together.