LH and FSH (Sex Hormones, Gonadotropins)
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are pituitary gonadotropins that govern the ovaries and testes — interpreting them together helps determine whether a fertility or cycle problem lies in the gonads themselves or higher up, in the brain.
Number of studies
2
Safety
Requires caution
Time to effects
Not applicable — LH and FSH are a diagnostic test, not an intervention.
Who it's for
Table of contents
TL;DR
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are pituitary gonadotropins that govern the ovaries and testes — interpreting them together helps determine whether a fertility or cycle problem lies in the gonads themselves or higher up, in the brain.
- →Helps distinguish primary (gonadal) hypogonadism from secondary (hypothalamic-pituitary) hypogonadism based on the hormonal pattern alone
- →Is a key element in diagnosing the causes of irregular or absent periods and suspected premature ovarian failure
- →Facilitates infertility workup in both partners by locating the problem at the correct level of the hormonal axis
| Test type | Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentration in blood serum |
|---|---|
| Level of evidence | Strong — a well-established pillar of hypothalamic-pituitary-gonadal axis diagnostics |
| Target group | People with menstrual disorders, infertility, suspected hypogonadism, or abnormal pubertal development |
| Key parameters | LH and FSH concentration (IU/L or mIU/mL), interpreted together and in the context of cycle day or age |
| Preparation | No strict fasting required; women must note cycle day and report hormonal contraceptive use |
| Status | A first-line diagnostic test for the hypothalamic-pituitary-gonadal axis, not a standalone fertility assessment tool |
Understand
Overview
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are glycoprotein gonadotropins secreted by gonadotroph cells of the anterior pituitary gland. Together they form the main link between the central nervous system and the gonads — the ovaries in women and the testes in men — governing puberty, the menstrual cycle, sperm production, and the synthesis of sex hormones, estradiol and testosterone. The test measures both hormones' concentrations in blood serum, usually simultaneously, since their relationship to each other and to cycle phase or age carries far more information than a single value taken in isolation.
The clinical significance of this test lies in the fact that the LH and FSH pattern helps locate where along the hypothalamic-pituitary-gonadal axis a problem sits. High concentrations of both gonadotropins alongside low sex hormone levels point to gonadal failure itself (primary, hypergonadotropic hypogonadism) — the pituitary correctly detects the estradiol or testosterone deficiency and tries to compensate with increased LH and FSH secretion, but the gonads don't respond. The opposite pattern — low or inappropriately normal LH and FSH with low sex hormones — points to a problem higher up, in the hypothalamus or pituitary (secondary, hypogonadotropic hypogonadism), where the driving signal itself is insufficient.
The test is most often ordered for women with irregular or absent periods, in the infertility workup of both partners, when premature ovarian failure or menopause is suspected, and in assessing puberty — both delayed and precocious. In men, LH and FSH are measured mainly in the workup of hypogonadism, infertility, and abnormal semen parameters, where they help distinguish a testicular cause from a hypothalamic-pituitary one.
Interpreting the result in women is especially context-dependent, since both hormones' concentrations change repeatedly over a single menstrual cycle. FSH is relatively highest at the start of the follicular phase, gradually declines as the dominant follicle matures, then both hormones surge sharply twelve to thirty-six hours before ovulation — it's this sharp LH surge that directly triggers ovulation. After ovulation, in the luteal phase, both hormones' concentrations decline again. For this reason, a single LH or FSH result only makes sense alongside the cycle day it was drawn on, and a test for early ovarian reserve is usually ordered on cycle day two or three. In postmenopausal women, both hormones, especially FSH, are persistently high, since the ovaries stop responding and the negative feedback from estradiol disappears.
In men, LH and FSH concentrations are much more stable over time than in women, though they still show pulsatile secretion on an hourly scale, which is why several measurements at short intervals are sometimes ordered when a single result is ambiguous. It's also worth knowing that the popular LH-to-FSH ratio, historically used in diagnosing polycystic ovary syndrome, has, according to more recent research, limited diagnostic value on its own and shouldn't be the sole diagnostic criterion.
Logistically, the test usually doesn't require strict fasting, but in women it's crucial to note the menstrual cycle day at the time of the draw, and the use of hormonal contraception or other hormone therapy should be reported to the ordering physician, since it strongly suppresses natural gonadotropin secretion and makes the result uninterpretable in the standard way.
It's worth emphasizing that this test evaluates only the laboratory parameter itself and the hormonal axis's regulatory mechanism — it doesn't replace a full fertility assessment or infertility workup, which covers a much broader range of clinical, imaging, and partner-based tests. LH and FSH are one piece of that puzzle, not the whole workup.
Mechanism of action
LH and FSH secretion is governed by the hypothalamic gonadotropin-releasing hormone (GnRH), released in a characteristic pulsatile fashion into the pituitary portal vessels. The frequency and amplitude of these GnRH pulses determine which of the two hormones the pituitary secretes relatively more of — faster pulsing favors relatively greater LH secretion, slower pulsing favors FSH, one of the mechanisms differentiating the pituitary's response across cycle phases and life stages.
Pituitary gonadotroph cells synthesize and release LH and FSH in response to GnRH, and the hormones themselves act on G-protein-coupled receptors in the gonads: LH stimulates Leydig cells in the testes to produce testosterone and theca cells of the ovary to produce androgens that are precursors of estrogens, while FSH stimulates Sertoli cells in the testes, which support spermatogenesis, and granulosa cells of the ovarian follicle, responsible for its growth and the conversion of androgens to estradiol.
The entire axis operates on a negative feedback basis — rising testosterone in men and estradiol in women (outside a brief periovulatory window) inhibits hypothalamic GnRH secretion and the pituitary's direct sensitivity to GnRH, limiting further LH and FSH secretion. In addition, inhibin B, produced by Sertoli cells in men and granulosa cells in women, selectively inhibits FSH secretion, making it a useful, though less commonly measured, marker of ovarian reserve and sperm-producing function.
A disturbance of this feedback loop at any point produces a characteristic, recognizable laboratory pattern. Damage or failure of the gonads themselves removes the inhibitory influence of sex hormones, so the hypothalamus and pituitary respond compensatorily with increased GnRH, LH, and FSH secretion — hence high gonadotropins with low sex hormones in primary hypogonadism. Damage to or suppression of the hypothalamus or pituitary itself — for example, by a tumor, significant energy deficit, chronic stress, or hyperprolactinemia suppressing GnRH secretion — lowers the driving signal at its source, giving low or inappropriately normal LH and FSH despite low sex hormones, i.e., the picture of secondary hypogonadism.
Pulsatile GnRH secretion from the hypothalamus
The frequency and amplitude of GnRH pulses determine the relative proportion of LH and FSH secreted by the pituitary.
LH and FSH action on gonadal target cells
LH drives androgen production (Leydig, theca cells), FSH supports spermatogenesis and follicle growth (Sertoli, granulosa cells).
Negative feedback via sex hormones and inhibin B
Testosterone and estradiol inhibit GnRH and LH/FSH secretion, while inhibin B selectively inhibits FSH alone.
Recognizable patterns of axis disturbance
Gonadal failure produces high LH/FSH with low sex hormones; hypothalamic or pituitary disturbance produces low or inappropriately normal LH/FSH with low sex hormones.
Evidence: strong — based on 2 studies in this database.
Benefits
Common myths
MythThe LH-to-FSH ratio alone is enough to diagnose polycystic ovary syndrome.
FactMore recent research consistently shows that the LH/FSH ratio has limited standalone diagnostic value in PCOS and shouldn't be the sole diagnostic criterion — diagnosis rests on broader clinical, hormonal, and imaging criteria.
MythA single LH and FSH measurement fully captures the true level of these hormones.
FactBoth hormones are secreted pulsatile on an hourly scale, and in women they also change significantly across the menstrual cycle, so interpreting a single result always requires accounting for cycle day and sometimes repeating the measurement.
MythHigh FSH always means menopause.
FactWhile persistently high FSH is typical of menopause, elevated values can also result from premature ovarian failure at a younger age, a state after gonad removal, or, in men, primary testicular failure, which is why it always requires interpretation in the context of age and clinical picture.
MythThe LH and FSH result doesn't depend on cycle day in women, so the test can be done at any time.
FactOn the contrary — cycle day is one of the most important pieces of interpretive context. Ovarian reserve assessment is usually done on cycle day two or three, and a result from a different day can be hard to interpret unambiguously.
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Practice
Frequently asked questions
For baseline ovarian reserve assessment, the test is usually ordered on cycle day two or three. A measurement at a different point in the cycle has a different reference value and is harder to interpret without precisely knowing the cycle phase.
This pattern points to primary hypogonadism, a problem in the gonads themselves — the ovaries or testes. The pituitary correctly detects the sex hormone deficiency and tries to compensate with increased gonadotropin secretion, but the gonads can't respond adequately.
This pattern suggests secondary hypogonadism, a problem at the level of the hypothalamus or pituitary — the driving signal is insufficient, even though the gonads themselves could respond correctly if given the right stimulus.
Yes, significantly — hormonal contraception suppresses the natural pulsatile secretion of LH and FSH, so a result obtained while on it doesn't reflect the true, endogenous functioning of the hypothalamic-pituitary-gonadal axis and requires different interpretation, or contraception should be stopped before testing if possible and safe.
No — it's one important piece of a broader workup that also includes other hormones, ovarian reserve assessment, semen analysis in men, and imaging evaluation, not a standalone, complete fertility test.
What to combine with
Good combinations
Testosterone — In men, LH and FSH are always interpreted together with testosterone to locate the cause of hypogonadism
Estradiol During TRT — What's the Normal Range, and Do You Need to Lower It? — In women, assessing estradiol together with LH and FSH helps confirm cycle phase or menopausal status
Prolactin (Blood Test) — Elevated prolactin suppresses GnRH secretion and secondarily lowers LH and FSH, so both tests are worth ordering together for unclear cycle disorders or infertility
Safety
Side effects & contraindications
Possible side effects
Contraindications
No significant contraindications at typical doses.
Interactions
In women, menstrual cycle phase determines the expected result range — the same LH or FSH level means something different in the follicular, periovulatory, and luteal phases
The pulsatile nature of both hormones' secretion on an hourly scale means a single measurement may not reflect the true, averaged level
Hormonal contraception and other hormone therapy strongly suppress natural LH and FSH secretion, making the result uninterpretable in the standard way
Significant physiological or psychological stress and significant energy deficit (e.g., from intense training or a restrictive diet) can suppress GnRH secretion and secondarily LH and FSH
Hyperprolactinemia suppresses pulsatile GnRH secretion, lowering LH and FSH independent of the gonads' own state
The postmenopausal state or after gonad removal permanently and significantly raises both hormones, which should be accounted for when interpreting results in older women
Is it worth taking?
Who it's for
- Women with irregular or absent periods, suspected premature ovarian failure, or in the perimenopausal period
- People being worked up for infertility, in either partner, as part of a broader hormonal assessment
- Men with suspected hypogonadism, abnormal semen parameters, or unexplained reduced libido
- Children and adolescents with delayed or precocious puberty, evaluated by a specialist physician
Not for
- No significant contraindications at typical doses.
Evidence
Worth knowing
A sharp LH surge twelve to thirty-six hours before ovulation directly triggers the release of the egg from the dominant follicle.
In men, LH stimulates Leydig cells to produce testosterone, while FSH stimulates Sertoli cells that support spermatogenesis — two separate, though related, pathways of action.
Inhibin B, produced by the gonads, selectively inhibits FSH secretion and serves as an additional marker of ovarian reserve or sperm-producing function.
High LH and FSH with low sex hormones points to a problem in the gonads themselves, while low or inappropriately normal LH and FSH with low sex hormones points to a problem in the hypothalamus or pituitary.
Studies
A reliable assessment of FSH and LH requires accounting for the cyclic and circadian fluctuations in gonadotropin secretion, not interpreting a single, isolated result.
Grigorova M, Punab M, Editorial: Follicle-Stimulating Hormone: Fertility and Beyond, Frontiers in Endocrinology, 2019
Reference intervals for serum testosterone, SHBG, LH and FSH in males from the NORIP project
Strong evidenceBjerner J, Biernat D, Fosså SD, Bjøro T · Scandinavian Journal of Clinical and Laboratory Investigation · 2009
Establishment of population-based reference intervals for LH, FSH, testosterone, and SHBG in men based on the large Scandinavian NORIP reference project.
View studyThe LH/FSH ratio has little use in diagnosing polycystic ovarian syndrome
Moderate evidenceCho LW, Jayagopal V, Kilpatrick ES, Holding S, Atkin SL · Annals of Clinical Biochemistry · 2006
A study comparing the LH/FSH ratio in women with PCOS versus a control group, showing limited diagnostic value of the ratio when used alone.
View studySources & bibliography
- Bjerner et al. 2009 — Scandinavian Journal of Clinical and Laboratory Investigation
- Cho et al. 2006 — Annals of Clinical Biochemistry
The PubMed identifiers in this knowledge base were checked against NCBI records (October 2026). If you spot an error in a source, please let us know via the contact form.
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About the authors of this entry
Author
Redakcja VitMode — Hormony i endokrynologiaEditorial team
VitMode Editorial — Hormones and Endocrinology is the VitMode editorial team responsible for: hormones, testosterone therapy, the thyroid and metabolism. The team has no individual bylines — texts are prepared by VitMode editors from primary sources (clinical trials, meta-analyses, guidelines). Every cited PubMed paper is automatically checked for a matching identifier, title and publication year. The content is educational and does not replace medical advice. Factual errors can be reported in a comment under the post or through the contact form; corrections are made by the editorial team.
328 publications on this site
Editorial review
Redakcja VitMode — Badania i biomarkeryEditorial team
VitMode Editorial — Lab Tests and Biomarkers is the VitMode editorial team responsible for: laboratory tests, interpreting results and ageing biomarkers. The team has no individual bylines — texts are prepared by VitMode editors from primary sources (clinical trials, meta-analyses, guidelines). Every cited PubMed paper is automatically checked for a matching identifier, title and publication year. The content is educational and does not replace medical advice. Factual errors can be reported in a comment under the post or through the contact form; corrections are made by the editorial team.
272 publications on this site
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