Reproductive Endocrinology & Gynecology & Urology & Family Medicine
Inhibin B
Inhibin B is a member of the TGF-β (Transforming Growth Factor-beta) superfamily, a homodimeric glycoprotein composed of an alpha subunit and a betaB subunit, produced in a gonad-specific manner. In women, it is primarily secreted by granulosa cells of early follicular phase (d2–d5) antral follicles under the influence of FSH. In men, it is produced exclusively by Sertoli cells of the seminiferous tubules. Inhibin B exerts selective negative feedback on pituitary FSH secretion (without affecting LH), thus constituting a key regulator of the hypothalamic-pituitary-gonadal axis. In clinical practice, its measurement is used in two main contexts: assessing ovarian reserve in women (alongside AMH and basal FSH) and evaluating spermatogenesis in infertile men (a marker of Sertoli cell function and active spermatogenesis). Compared to AMH—which is currently the gold standard marker for ovarian reserve—inhibin B exhibits greater intercycle variability and lower sensitivity for detecting diminished ovarian reserves. However, it retains real clinical utility, particularly in the evaluation of male infertility and in certain pediatric contexts (assessment of puberty and testicular function).
Biochemistry, Regulation, and Reference Values
- Molecular structure, synthesis, and regulation of inhibin B: Biochemical structure: member of the TGF-β superfamily → inhibin B = α-βB heterodimer (18 kDa per subunit) + inhibin A = α-βA heterodimer → activin = βA-βA or βB-βB homodimer (without an α subunit) → follistatin neutralizes activin (and partially inhibin) in tissues → inhibin B and inhibin A share the same α subunit but differ in their β subunit → this structural difference explains their distinct secretion profiles during the menstrual cycle + in women — secretion and cyclic profile: granulosa cells of antral follicles → main source of inhibin B in the early follicular phase → inhibin B is produced in response to FSH stimulation → peak inhibin B in the early follicular phase (D2–D7) → declines after the LH surge → inhibin A: produced during the luteal phase → by the corpus luteum + dominant follicle at the end of the follicular phase → peak in the mid-luteal phase → negative feedback of inhibin B on pituitary FSH: inhibin B secreted by antral follicles → selectively inhibits FSH secretion → NO effect on LH → reduction in FSH → limits follicular recruitment → mechanism regulating the number of follicles recruited per cycle → measurement of inhibin B indirectly reflects the pool of antral follicles (ovarian reserve) → in men — secretion and regulation: Sertoli cells (only) → inhibin B is the serological marker of Sertoli cell function + active spermatogenesis in the seminiferous tubules → regulation: FSH stimulates the production of inhibin B by Sertoli cells → inhibin B in turn inhibits FSH secretion → feedback loop → high FSH + low inhibin B = insufficient feedback → impaired spermatogenesis → testosterone (Leydig cells) has a permissive effect on inhibin B production by Sertoli cells → integration of the LH/testosterone + FSH/inhibin B axis; reference values (vary by laboratory — ELISA or CLIA immunoenzymatic method): women of reproductive age (days 2–5 of the cycle): 15–300 pg/mL (depending on the laboratory and method) → gradual decrease with age → inhibin B <45 pg/mL on Day 3 → decrease in ovarian reserve → undetectable inhibin B (<10–15 pg/mL) → menopause + severe ovarian insufficiency → note: AMH is now preferred over inhibin B for assessing ovarian reserve (longer half-life + less intercyclic variability + measurable at any time in the cycle vs. inhibin B = D2–D5 only) + adult male: 80–350 pg/mL (depending on the laboratory) → inhibin B <80 pg/mL → impaired spermatogenesis → undetectable inhibin B (<15–20 pg/mL) + azoospermia + very high FSH → severe failure of spermatogenesis (severe non-obstructive azoospermia) → very poor prognosis for TESE + prepubertal child: low in girls (often undetectable) → detectable in boys (produced by immature Sertoli cells — marker of the presence of functional testicular tissue)
- Main Clinical Indications and Comparison with AMH: Indication 1 — Assessment of ovarian reserve in women: Inhibin B vs. AMH: AMH is currently the gold standard marker of ovarian reserve (produced by the granulosa cells of preantral and early antral follicles + stable throughout the cycle + longer half-life + less affected by hormonal contraception) → Inhibin B has greater inter-cycle variability + must be measured on days 2–5 only → In the context of ovarian reserve assessment, inhibin B is now considered a second-line marker behind AMH and AFC (antral follicle count) → However, in certain situations where AMH is unavailable or its results are discordant, inhibin B retains complementary diagnostic value → Seifer 1997 — Journal of Clinical Endocrinology and Metabolism: inhibin B on day 3 <45 pg/mL → decreased ovarian reserve + poorer IVF outcomes → foundational data + Groome 1996 — Journal of Clinical Endocrinology and Metabolism: development of the inhibin B assay → validation of the method → indication 2 — assessment of spermatogenesis in male infertility: inhibin B = marker of Sertoli cell function and tubular spermatogenesis → correlates with sperm concentration and motility (Sharpe 1994 — Journal of Endocrinology + Pierik 1998 — Clinical Endocrinology) → low inhibin B + high FSH → impaired spermatogenesis → probable non-obstructive (secretory) azoospermia → predictive value for TESE (surgical sperm extraction): inhibin B >80 pg/mL → probability of finding sperm with TESE: 60–70 % → undetectable inhibin B + FSH >15 IU/L → probability of finding sperm with TESE: <15–20 % → borderline prognosis for TESE → Ballesca 2000 — Human Reproduction: inhibin B + prediction of residual spermatogenesis in non-obstructive azoospermia + indication 3 — assessment of puberty and pediatric gonadal function: in boys: inhibin B is detectable as early as the neonatal period (mini-puberty) → then remains detectable during prepuberty + increases sharply during puberty (stimulation by FSH) → its measurement helps assess testicular tissue integrity and the presence of functional Sertoli cells → useful in the differential diagnosis of delayed puberty (detectable inhibin B → Sertoli cells present → testicular tissue present) vs. anorchism + in girls: inhibin B often undetectable during prepuberty → appears at puberty + indication 4 — ovarian and testicular tumors (ancillary tumor marker): ovarian granulosa cell tumors (GCTs): both inhibin B and inhibin A are very elevated → used as monitoring markers (response to treatment + recurrence) → Burger 2001 — Journal of Clinical Endocrinology and Metabolism: inhibin B + granulosa cell tumors + follow-up + Sertoli cell tumors (testes): inhibin B may be elevated
Clinical Applications of Inhibin B
| Clinical context | Data, interpretation and action | Key studies and recommendations |
|---|---|---|
| Inhibin B and ovarian reserve in women Ovarian reserve — AMH — basal FSH — AFC — inhibin B day 3 — IVF results — menopause — POI — ovarian aging — menstrual transition — inhibin B pregnancy |
Inhibin B in the context of ovarian reserve: inhibin B profile according to reproductive status: women of childbearing age with normal ovarian reserve: inhibin B on day 3: 80–200 pg/mL → peak in the early follicular phase (days 5–7) → predominant inhibin A in the luteal phase + low inhibin B at perimenopause: inhibin B declines gradually before FSH and before estrogen fluctuations → the reduction in inhibin B is an early marker of the reduction in the follicular pool → Burger 2000 — Journal of Clinical Endocrinology and Metabolism: inhibin B + menopausal transition → decline in inhibin B precedes the rise in FSH + the reduction in estrogen → early marker of ovarian aging + in established menopause: undetectable inhibin B → very high FSH (>40 IU/L) → absence of follicular activity + premature ovarian insufficiency (POI): undetectable or very low inhibin B + FSH >25 IU/L on two occasions + amenorrhea >4 months in a woman <40 years old → correlation with AMH (both severely reduced) + inhibin B in the evaluation of response to ovarian stimulation (IVF): inhibin B on Day 3 predicts ovarian response to stimulation: inhibin B <45 pg/mL → diminished reserve → poorer response to FSH → fewer recruited follicles → fewer retrieved oocytes → reduced IVF success rate → Seifer 1997 — JCEM: inhibin B on day 3 <45 pg/mL → correlates with poorer IVF outcomes → however: AMH and CFA are now preferred over inhibin B for predicting ovarian response (better diagnostic performance + less variability) + inhibin B and pregnancy: rises slightly in the 1st trimester → produced by the corpus luteum (first weeks) + by the cytotrophoblast → returns to preconception levels in the 2nd trimester → inhibin B decreases during pregnancy (cytotrophoblast produces little inhibin B vs. inhibin A, which is elevated in preeclampsia); summary of the role of inhibin B in current ovarian reserve assessment (2024): first-line assessment: AMH + basal FSH (D2–D5) + antral follicle count (AFC) by ultrasound → second-line or supplemental assessment: inhibin B on D3 if AMH is discordant or unavailable → the trend in current guidelines (ESHRE 2023 + SOGC 2022) is to no longer recommend routine use of inhibin B in ovarian reserve testing—as AMH has largely replaced it—and inhibin B retains value in research contexts, granulosa cell tumors, menopause assessment, and the menopausal transition | Seifer, 1997 — Journal of Clinical Endocrinology and Metabolism: Inhibin B <45 pg/mL + diminished ovarian reserve + IVF results → foundational data + Groome, 1996 — JCEM: Development and validation of an enzyme immunoassay for inhibin B + Burger, 2000 — JCEM: Inhibin B + menopausal transition → Inhibin B decline precedes FSH rise → early marker of decreased reserve + La Marca, 2009 — Human Reproduction Update: AMH vs. Inhibin B → AMH superior for ovarian reserve assessment + better correlation with AFC + less variability → AMH = reference marker + ESHRE, 2023 + SOGC, 2022: Ovarian reserve → AMH + FSH + AFC = first-line assessment → Inhibin B = second-line + Broer, 2011 — Human Reproduction Update: Meta-analysis → AMH and AFC superior to Inhibin B and FSH for predicting ovarian stimulation response + CSFA (Canadian Fertility and Andrology Society) + INESSS Québec: AMH and Inhibin B assay in infertility assessment |
| Inhibin B in male infertility and azoospermia Spermatogenesis - Sertoli cells - non-obstructive azoospermia - obstructive azoospermia - TESE - FSH inhibin B - varicocele - cryptorchidism - Klinefelter - chemotherapy - hypogonadism |
Inhibin B in male infertility — role as a marker of spermatogenesis: physiological basis: Sertoli cells → inhibin B → FSH feedback → inhibin B correlates directly with the number of functional Sertoli cells and the status of spermatogenesis → combined clinical interpretation of inhibin B + FSH + testosterone: normal inhibin B (>80 pg/mL) + normal FSH + normal testosterone → normal spermatogenesis expected → azoospermia if present → likely obstructive (CBAVD + obstruction of the vas deferens) → low inhibin B (40–80 pg/mL) + slightly elevated FSH → moderate impairment of spermatogenesis → probable oligospermia + very low inhibin B (<40 pg/mL) + elevated FSH (>10 IU/L) → severely impaired spermatogenesis → severe oligospermia or non-obstructive azoospermia → undetectable inhibin B + very high FSH (>15–20 IU/L) + normal or low testosterone → total failure of spermatogenesis → secretory azoospermia → poor prognosis for TESE → Pierik 1998 — Clinical Endocrinology: inhibin B + azoospermia → discriminating marker for obstructive vs. non-obstructive azoospermia → Ballesca 2000 — Human Reproduction: inhibin B + prediction of residual spermatogenesis → threshold value of 80 pg/mL for differentiation + predictive value for TESE (surgical testicular sperm extraction): inhibin B can guide the decision to perform TESE in non-obstructive azoospermia → inhibin B ≥80 pg/mL → probability of finding sperm with TESE: 60–70 % → inhibin B <40 pg/mL → probability of finding sperm: 30–40 % → undetectable inhibin B → very low probability (<15–20 %) → BUT: inhibin B alone is not sufficient → limited value → TESE should not be refused solely on the basis of undetectable inhibin B (sperm may be found despite very low inhibin B) → the decision to perform TESE must take into account the clinical context + genetics (karyotype + Y-chromosome microdeletions + CFTR) + causes of low inhibin B in male infertility: secretory azoospermia (non-obstructive): Klinefelter syndrome (47,XXY) + Y-chromosome microdeletions (AZFa + AZFb + AZFc) + bilateral cryptorchidism + orchitis + alkylating chemotherapy + testicular radiation therapy + idiopathic → varicocele: moderately reduced inhibin B → improvement after varicocelectomy correlates with increased inhibin B → Alukal 2010 — Urology + hypogonadotropic hypogonadism (HH): GnRH deficiency → low FSH + LH → low testosterone → low inhibin B → treatment: hCG + recombinant FSH → stimulates spermatogenesis + inhibin B production → treatment response monitored by inhibin B + LH and testosterone + cryptorchidism: if bilateral + untreated → progressive reduction in Sertoli cells → low inhibin B → indicator of residual testicular damage | Pierik 1998 — Clinical Endocrinology: inhibin B + azoospermia → discriminate obstructive vs. non-obstructive azoospermia → diagnostic reference + Ballesca 2000 — Human Reproduction: inhibin B + prediction of residual spermatogenesis in non-obstructive azoospermia → 80 pg/mL threshold + Sharpe 1994 — Journal of Endocrinology: review of Sertoli cell function + role of inhibin B + Alukal 2010 — Urology: varicocele + inhibin B + improvement post-varicocelectomy + Jensen 1997 — European Journal of Endocrinology: inhibin B + spermogram + correlation + Cooper 2021 — Human Reproduction (WHO 6th edition): spermogram standards + etiological workup of male infertility + EAU 2023 (European Association of Urology): male infertility guidelines → inhibin B + FSH + testosterone → reference workup + AUA guidelines male infertility 2021 + SCFA (Canadian Fertility and Andrology Society): male infertility workup in Canada + INESSS Quebec: reimbursement of inhibin B in infertility workup |
| Inhibin B in Pediatrics, Granulosa Cell Tumors, and Special Situations Puberty — mini-puberty — delayed puberty — anorchidism — granulosa cell tumors — hypogonadism — inhibin B chemotherapy — fertility preservation — pediatric cryptorchidism — anti-Müllerian |
Inhibin B in pediatrics — a marker of puberty and gonadal function: in boys: inhibin B is present at birth → increases during mini-puberty (2–6 months of life) → reflects neonatal activation of the HPG axis + then remains stable (barely detectable) until puberty → sharp increase at puberty due to FSH → allows assessment of the presence of functional testicular tissue (active Sertoli cells) → useful in the differential diagnosis between: constitutional delayed puberty (detectable inhibin B + low FSH) → permanent hypogonadotropic hypogonadism (very low or undetectable inhibin B if no FSH stimulation) → anorchism (undetectable inhibin B + undetectable AMH + elevated FSH) → bilateral cryptorchidism (moderately low inhibin B depending on the degree of involvement) → Bergadà 2006 — Clinical Endocrinology: inhibin B + marker of testicular tissue presence in cases of non-palpable gonads in children (useful with AMH to diagnose anorchism vs. bilateral cryptorchidism — no need for surgical exploration if inhibin B and AMH are undetectable) → in girls: inhibin B generally undetectable before puberty → appears at puberty → rarely used in pediatric practice vs. AMH, which is better standardized; inhibin B after chemotherapy or radiation therapy — fertility preservation: alkylating chemotherapy (cyclophosphamide + cisplatin + carmustine) + pelvic or testicular radiation therapy → destroy Sertoli cells + spermatogonia → sustained reduction in inhibin B → marker of treatment-induced gonadal damage → monitoring of spermatogenesis recovery after treatment: inhibin B levels rise → sign of Sertoli cell recovery → correlates with the resumption of spermatogenesis → measuring inhibin B levels 6–12 months post-chemotherapy provides guidance on the likelihood of fertility recovery → Wallace 2005 — Human Reproduction: inhibin B + chemotherapy + marker of gonadal damage + recovery of spermatogenesis; ovarian granulosa cell tumors (GCTs): inhibin B + inhibin A are the most specific tumor markers for GCs → excessive production → very high inhibin levels → FSH inhibition → absence of menstrual cycle + intermenstrual bleeding + pelvic mass + precocious puberty if pediatric → diagnosis and follow-up: inhibin B + inhibin A measured at diagnosis + at each follow-up visit → Burger 2001 — JCEM: inhibin B + inhibin A + granulosa cell tumors → markers for follow-up + recurrence → sensitivity: inhibin A is superior to inhibin B as a follow-up marker for adult GCs → inhibin B is more useful in juvenile (pediatric) GCs → follow-up with inhibin B + AMH + inhibin A + pelvic ultrasound every 3–6 months | Bergadà 2006 — Clinical Endocrinology: inhibin B + AMH + child + nonpalpable gonads → differential diagnosis of anorchia vs. cryptorchidism → pediatric referral + Burger 2001 — Journal of Clinical Endocrinology and Metabolism: inhibin B + inhibin A + granulosa cell tumors + follow-up + recurrence + Wallace 2005 — Human Reproduction: inhibin B + chemotherapy + marker of gonadal damage + spermatogenesis recovery + Sharpe 1994 — Journal of Endocrinology: Sertoli cells + inhibin B + development + Jensen 1997 — EJE: inhibin B + spermogram + correlation → reference + La Marca 2009 — Human Reproduction Update: inhibin B vs. AMH → AMH superior + ESHRE 2023: inhibin B in pediatric assessment + Scfa + SOGC 2022: inhibin B in ovarian reserve assessment → second-line + EAU 2023 + AUA 2021: inhibin B in male infertility assessment + INESSS Quebec: inhibin B coverage in indicated contexts + Endocrine Society 2018: management of male hypogonadism + inhibin B in follow-up |
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Inhibin B is the serological marker of Sertoli cell function in men — undetectable inhibin B associated with very high FSH indicates severe spermatogenesis failure, but does not formally contraindicate TESE. In women, AMH has largely replaced inhibin B as the gold standard marker for ovarian reserve (more stable, measurable at any point in the cycle). Inhibin B remains useful in the evaluation of male infertility, monitoring granulosa cell tumors, and assessing pediatric gonadal function (with AMH, to differentiate anorchia from bilateral cryptorchidism).
Situations requiring urgent specialist consultation
Prepubertal boy with bilaterally non-palpable gonads + undetectable inhibin B + undetectable AMH + elevated FSH → Probable bilateral anorchia → Pediatric urology consultation + genetics → Exploratory laparoscopy for confirmation → No functional testicular tissue → Testosterone replacement at puberty + psychological counseling → If inhibin B + AMH detectable → Testicular tissue present → High bilateral cryptorchidism → Urgent surgical orchiopexy.
35-year-old female with amenorrhea for 6 months + FSH >25 IU/L + undetectable inhibin B + collapsed AMH (<0.5 pmol/L) + hot flashes → Probable premature ovarian insufficiency (POI) → endocrinological + gynecological consultation → further workup (karyotype + FMR1 + anti-ovarian antibodies) + hormone replacement therapy (HRT) + fertility preservation if pregnancy desired (oocyte donation) → bone densitometry.
Woman with pelvic mass + metrorrhagia + very high inhibin B (>500 pg/mL) + high inhibin A + low FSH → Probable granulosa cell tumor (GCT) → Urgent gynecologic oncology consultation → Pelvic ultrasound + MRI + CA-125 + inhibins → Excisional surgery → Follow-up with inhibin B + inhibin A every 3-6 months post-surgery.
Patient treated for cancer with alkylating chemotherapy or pelvic radiotherapy, with inhibin B collapsed at 6 months post-treatment + azoospermia + very high FSH → Severe gonadal damage post-chemotherapy → Andrology + Reproductive Endocrinology consultation → If cryopreservation was performed before treatment → Use of frozen sperm for ART → If no cryopreservation → TESE based on availability and prognosis → Monitor spermatogenesis recovery with inhibin B every 6 months.
Consult at Clinique Omicron
Clinique Omicron physicians prescribe and interpret inhibin B levels as part of the ovarian reserve assessment (alongside AMH + FSH + AFC), male infertility assessment (in combination with semen analysis + FSH + testosterone), monitoring of granulosa cell tumors, and evaluation of pediatric gonadal function. They refer patients to appropriate specialists (gynecologist + urologist + endocrinologist + oncologist) based on the results. Consultations are available at several service points in Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
The content of this page is provided for informational purposes only and does not substitute for the advice of a physician, endocrinologist, or specialist in reproductive medicine. The interpretation of inhibin B should always be carried out within the full clinical context, integrating other markers of gonadal function.
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