Inhibin B: Mechanism, Dosing & Research Data

Inhibin B is the alpha/beta-B dimeric form of inhibin, the dominant FSH-suppressing hormone in males and during the follicular phase in females. In males, it is produced by Sertoli cells in proportion to functional spermatogenesis and serves as the most specific biomarker of Sertoli cell function and sperm production capacity. Low inhibin B in infertile males predicts azoospermia with high accuracy.

Mechanism of Action

Male: Sertoli cell inhibin B is the primary paracrine signal of spermatogenesis; produced in proportion to germ cell content of seminiferous tubules
Inhibin B directly correlates with testicular volume and sperm count; as germ cell mass decreases, inhibin B falls and FSH rises (loss of negative feedback)
Female follicular phase: developing granulosa cells of antral follicles produce inhibin B; FSH stimulates inhibin B rise which then suppresses further FSH, creating the midfollicular FSH nadir
Betaglycan presentation to ACVR2A: same receptor mechanism as inhibin A; beta-B form slightly different potency at betaglycan vs beta-A form
Inhibin B/FSH ratio: combined marker more predictive of testicular sperm extraction (TESE) outcome than either alone in azoospermia

Research Findings

Male infertility: inhibin B below 80 pg/mL predicts non-obstructive azoospermia with 90% sensitivity; lowest levels (<20 pg/mL) almost invariably indicate Sertoli-cell-only syndrome
TESE prediction: serum inhibin B in azoospermic males correlates with probability of finding sperm on testicular biopsy; values >60 pg/mL suggest higher TESE success
Childhood: inhibin B rises dramatically in boys at mini-puberty (3-6 months) and again at puberty, marking Sertoli cell activation; absent mini-puberty rise suggests bilateral cryptorchidism or anorchia
Chemotherapy monitoring: inhibin B falls before FSH rises after gonadotoxic therapy; earlier indicator of spermatogenic damage
Granulosa cell tumor (female): inhibin B elevated in some GCTs; both inhibin A and B measured for comprehensive monitoring

Research Protocols

Male fertility workup: serum inhibin B with FSH, LH, testosterone; inhibin B reference range adult males 80-300 pg/mL (assay-dependent)
Pediatric cryptorchidism: inhibin B at 3-6 months of age to confirm testicular function (anorchia if undetectable and no testosterone rise)
TESE counseling: inhibin B + FSH + testicular volume to predict TESE success probability before recommending surgery
Chemotherapy follow-up: inhibin B at 6, 12, 24 months after gonadotoxic therapy; recovery indicates spermatogenesis resumption

Interactions

FSH: inverse relationship; FSH rises as inhibin B falls; combined FSH + inhibin B provides more complete picture of gonadal function than either alone
Activin B: functional antagonist of inhibin B at pituitary; both share the beta-B subunit but differ in dimerization partner
AMH: in males, AMH + inhibin B from Sertoli cells comprehensively assess Sertoli cell function; both should fall with seminiferous tubule damage

Safety Profile

Endogenous glycoprotein; not therapeutically administered. Serum measurement is a routine safe diagnostic test. Central role as male Sertoli cell biomarker and female follicular phase hormone. Not administered exogenously.