Luteinizing Hormone (LH)
LH is a brain hormone that tells the ovaries or testes what to do — in women, a mid-month burst of it is the signal that releases an egg. Its level swings a lot through the month, so there is no single "normal" number. Your result only makes sense read against where you are in your cycle and your other hormones, which is exactly how your GP looks at it.
Targeted TestingWhat is luteinizing hormone (lh)?
Luteinising hormone (LH) is made by the pituitary gland — a small gland at the base of the brain that controls many of the body's hormone systems. Its production is part of a complex feedback loop involving hormones from the gonads (ovaries or testes), the pituitary itself, and the hypothalamus — a region of the brain — through a signal called gonadotrophin-releasing hormone (GnRH). In women, LH works together with follicle-stimulating hormone (FSH) to regulate the menstrual cycle. FSH stimulates cells around the eggs in the ovaries to produce oestradiol; when oestradiol reaches a certain level the pituitary sends a sudden surge of both FSH and LH, and this surge triggers ovulation — the release of the egg from the ovary. In men, LH signals the testes to produce testosterone and plays a role in sperm production alongside FSH.
Why is it tested?
Your GP may order an LH test to investigate fertility concerns, irregular or absent periods, or symptoms that suggest a hormone imbalance. It is usually measured alongside FSH, oestradiol and sometimes progesterone and testosterone, rather than on its own. One important nuance worth knowing: routine measurement of LH for fertility investigation is of limited value in most women, except in early menopause. The clinical picture and cycle timing guide whether and when the test adds useful information.
Reference range (Australia)
LH peaks mid-cycle (the surge that triggers ovulation) and otherwise varies by cycle phase; in men it is comparatively steady. The report's phase-specific interval is the relevant comparison.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A below-range LH is easier to explain in context. In the early part of the cycle, or while taking hormonal contraception (such as the pill, implant, or injection), LH naturally sits low — so a low result may simply reflect where you are in your cycle or your current medications. Persistently low LH across the cycle may point to the pituitary not sending its signal properly; your GP can weigh that against your symptoms and other hormone results.
An in-range LH result, read against the phase-specific interval on your report, suggests the pituitary is sending its hormone signal as expected. Interpretation still depends on where you are in your cycle — your GP will factor that in.
A high LH on its own rarely means something is wrong, and timing explains most of it. LH is naturally high during the mid-cycle surge — if your blood was drawn around that time, an above-range reading may simply reflect ovulation being triggered. Outside the surge window, a persistently high LH can point to the ovaries or testes being less responsive to the hormone's signal. In women this can occur as menopause approaches or with certain ovarian conditions; in men a consistently high LH alongside low testosterone can indicate a testicular problem. Your GP will read this alongside FSH, oestradiol, and the timing of your test.
What can affect your result
The biggest driver of LH is the menstrual cycle itself. LH sits lower and steady in the first half of the cycle (the follicular phase), then rockets to a sharp mid-cycle peak — the LH surge — before falling again in the second half (the luteal phase). A blood draw timed at the wrong moment can look dramatically different from one taken a day earlier or later. As menopause approaches, the ovaries become less responsive to LH and FSH, so both hormones rise over time. Hormonal contraception (the pill, implant, hormone-releasing IUD) suppresses the LH surge, which is how it prevents ovulation. Stress, significant weight changes, intense exercise, and conditions affecting the pituitary gland — such as prolactinomas (benign pituitary tumours that overproduce prolactin) or other pituitary problems — can all affect how much LH is released.
When to act
If your LH sits outside the reference interval, that is worth a chat with your GP, not a reason to worry immediately. They will want to know where you were in your cycle when the blood was drawn — that context is essential before drawing any conclusions. If you are investigating irregular periods, fertility concerns, or approaching menopause, your GP can guide whether a repeat test at a specific cycle phase would add clarity. It is also worth knowing that a single LH reading rarely tells the full story on its own; your GP will read it alongside FSH, oestradiol, and your symptoms. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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