LH & FSH Blood Test UK: What Your Gonadotrophins Are Telling You

What LH and FSH are, and the loop they run

LH and FSH are called gonadotrophins because they act on the gonads, the ovaries and testes. Both are made in the pituitary, a small gland at the base of the brain, which releases them in pulses under the command of a signal called GnRH from the hypothalamus above it. The physiology of GnRH and gonadotrophin secretion describes a chain of command: hypothalamus to pituitary to gonad, with the sex hormones produced at the end feeding back to dial the whole thing up or down.

That feedback loop is the key to reading the test. When the ovaries or testes are producing plenty of sex hormone, that hormone tells the pituitary to ease off, so LH and FSH stay low. When the gonad falters and the sex hormone falls, the pituitary senses the shortfall and pushes harder, so LH and FSH climb. A high gonadotrophin level is therefore not the gland failing. It is the gland shouting at an organ that has stopped answering.

What LH and FSH do in men

In men the two hormones divide the work. LH acts on the Leydig cells of the testes and is the direct trigger for testosterone production, which is why luteinising hormone physiology is so closely tied to male hormone health. FSH acts on the Sertoli cells and drives sperm production. So a man's LH speaks mainly to his testosterone, and his FSH speaks mainly to his fertility, though the two overlap.

This is why LH and FSH belong on a male hormone panel rather than a testosterone test alone. A low testosterone result means something very different depending on what the gonadotrophins are doing alongside it, a distinction the next section unpacks and the single most clinically useful reason to measure them. Our guide to low testosterone symptoms in men covers the symptoms that usually prompt the test.

What LH and FSH do in women

In women the gonadotrophins run the menstrual cycle. In the first half FSH recruits and matures a batch of ovarian follicles, which in turn produce oestradiol. As oestradiol peaks it triggers a sharp surge in LH, and that surge is what releases the egg at ovulation. After ovulation both fall back, and if no pregnancy follows the cycle resets. Because of this rhythm, a woman's LH and FSH change by the day, which is why the day of testing matters so much, covered later in this guide.

The same two hormones become central again at the other end of reproductive life. As the ovaries run low on follicles through perimenopause, they make less oestradiol, the feedback brake comes off, and FSH in particular climbs. That rising FSH is one of the classic laboratory signatures of the menopause transition, and our perimenopause blood test guide sets it in the wider picture of the markers that shift in those years.

The pattern that matters: where the problem sits

Here is the reason clinicians measure LH and FSH at all. Suppose a sex hormone is low, low testosterone in a man, or low oestradiol with absent periods in a woman. The gonadotrophins tell you where the fault lies, and there are two very different answers.

If LH and FSH are high while the sex hormone is low, the pituitary is doing its job and shouting, but the gonad is not answering. This is called primary hypogonadism, a problem in the testes or ovaries themselves. The European Association of Urology guidance on male hypogonadism uses exactly this split to separate the two types. In women, high FSH and LH with low oestradiol is the picture of the ovaries winding down, whether through menopause or, earlier than expected, premature ovarian insufficiency.

If LH and FSH are low or inappropriately normal while the sex hormone is also low, the gonad is capable but is not being told to work. This is secondary hypogonadism, a problem upstream in the pituitary or hypothalamus. Causes range from high prolactin to certain medications, significant stress, very low body fat, or a pituitary issue. This is the pattern that would send a clinician towards a prolactin test and a wider look at pituitary function. One pair of numbers, two completely different routes of investigation, which is why a sex hormone is rarely worth measuring without them.

FSH and the menopause: useful, but not for everyone

A high FSH is one of the best-known signs of the menopause, but the guidance on when to actually test it surprises people. UK guidance from NICE on menopause advises that for women over 45 with typical symptoms, the diagnosis is made on symptoms alone and an FSH test is not usually needed. The number can be misleading in perimenopause anyway, because it swings from one cycle to the next while the ovaries are still sputtering on.

Where FSH earns its place is in younger women. A persistently raised FSH in a woman under 40 with irregular or absent periods is part of how premature ovarian insufficiency is investigated, and it usually needs repeating to confirm. The full menopause marker picture, oestradiol included, sits in our menopause blood test guide.

The LH to FSH ratio in PCOS

In polycystic ovary syndrome the gonadotrophins often tilt. Many women with PCOS run an LH that sits high relative to FSH, sometimes described as a raised LH to FSH ratio. It reflects the disordered signalling that disrupts ovulation and is part of why periods become irregular. It is worth being clear that this ratio is a supporting observation rather than a diagnostic test on its own: the NHS describes PCOS as a diagnosis built from symptoms, scan findings and a fuller hormone picture together.

That fuller picture is the point. LH and FSH are read alongside testosterone, SHBG and the free androgen index in a PCOS work-up, not in isolation, and our PCOS blood test guide walks through the whole set and what each one adds.

LH, FSH and fertility

Both hormones sit at the centre of a fertility assessment for either sex. In women, a day-three FSH gives a rough read on ovarian reserve, the pool of eggs remaining, with a higher value suggesting the ovaries are working harder for less. In men, FSH speaks to sperm production and LH to testosterone, so a man with poor sperm results and a high FSH points towards a testicular cause, while low gonadotrophins point upstream. The NHS overview of infertility sets out where hormone blood tests fit in the wider assessment.

A guide does not replace clinical care here, and fertility investigation is rightly led by a specialist. What a blood test does offer is an early, private read on the hormone pattern, which is what our fertility blood test guide is built around.

How to take the test so the result means something

For women, timing is everything. To get a baseline read on FSH and LH, the sample is usually taken early in the cycle, around days two to five, counting from the first day of a period. Test in the middle of the cycle and you may catch the LH surge that triggers ovulation, which is a normal spike but useless as a baseline and easily misread. If cycles are irregular or have stopped, the timing rules change, and our guide to when to take a hormone blood test covers the alternatives.

For men the cycle issue does not apply, but timing still helps, because LH drives testosterone and testosterone is highest in the morning. A morning sample, ideally before about 11am, keeps the gonadotrophins comparable with the testosterone read against them. Either way, because the pituitary releases these hormones in pulses, a single borderline result is often worth repeating rather than acted on straight away.

Reference ranges, and why context decides the number

UK laboratories report LH and FSH in international units per litre (IU/L). For men, both typically sit in a broad band of roughly 1.5 to 12 IU/L, though laboratories differ. For women the picture is not a single range at all but several, because the normal value depends entirely on where she is. In the early follicular phase FSH usually sits in single figures, around the LH surge both jump, and after the menopause FSH commonly rises above about 30 IU/L and often much higher. These figures vary by assay, which is exactly why the range printed on your own report takes precedence over any number quoted in a guide.

More than almost any other blood test, LH and FSH cannot be read as a bare number. The same FSH of 20 IU/L is unremarkable in a postmenopausal woman, concerning in a 30-year-old with regular cycles, and meaningless without a date in someone mid-cycle. The figure only becomes information once you add the person's sex, age, cycle day or menopausal status, and the sex hormone sitting beside it. That is the whole case for reading them inside a panel rather than ordering one in isolation.

Frequently asked questions