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Inhibin B

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Inhibin B – A Marker of Ovarian and Testicular Function

Inhibin B is a glycoprotein synthesized in:

  • Sertoli cells of the seminiferous tubules in men
  • Granulosa cells of ovarian follicles in women

It belongs to the Transforming Growth Factor Beta (TGF-β) superfamily and consists of α- and β-subunits linked by disulfide bonds.

Inhibin B inhibits follicle-stimulating hormone (FSH) production in the pituitary gland through negative feedback and plays a local (paracrine) role in the testes and ovaries.

  • Gonadotropin-releasing hormone (GnRH) decreases inhibin B production.
  • Androgens, FSH, and insulin-like growth factor-1 (IGF-1) stimulate inhibin B secretion.
     

    Inhibin B in Women

  • Produced by antral (secondary) ovarian follicles.
  • Levels increase during puberty in girls.
  • Plays a key role in diagnosing precocious puberty and assessing gonadal maturity.
  • In reproductive-age women, levels fluctuate during the menstrual cycle:
    • Rise in the early follicular phase, peaking mid-phase.
    • Remain low during the luteal phase.
    • Brief peak occurs ~2 days after the LH surge, marking ovulation.
  • Helps regulate FSH levels during the early and mid-follicular phase.
  • Fasting is not required, but avoid eating 2–3 hours before the test (water is allowed).
  • Stop estrogen and androgen intake 48 hours before testing.
  • For women with regular cycles, the test is performed on days 3–4 of the cycle.
  • Avoid physical and emotional stress 30 minutes before the test.
  • No smoking for 3 hours before the test.
  • Diagnosis of granulosa cell and mucinous ovarian tumors
  • Monitoring ovarian tumors
  • Assessing ovarian reserve
  • Predicting IVF (in vitro fertilization) outcomes
  • Evaluating testicular function and spermatogenesis
  • Differentiating cryptorchidism from anorchia
  • Diagnosing disorders of sexual development
  • Screening for granulosa cell ovarian cancer (before, during, and after treatment)
  • Early or delayed puberty
  • Male and female infertility
  • Gonadal abnormalities in boys
  • Planning assisted reproductive techniques
  • Ambiguous genitalia in newborns (alongside other hormonal and imaging tests)

Causes of Increased Inhibin B Levels

In Women:

  • Granulosa cell ovarian tumors (89–100% of cases, with a 60-fold increase in Inhibin B)
  • Mucinous ovarian tumors (55–60% of cases)
  • Non-mucinous epithelial ovarian tumors (15–35% of cases)
  • Ovarian hyperstimulation syndrome (OHSS)
     

    Causes of Decreased Inhibin B Levels

    In Women:

  • Age-related ovarian reserve decline
  • Premature ovarian insufficiency
  • Menopause
  • Ovarian removal (oophorectomy)
  • Chemotherapy for cancer
  • Anorexia

  • In Men:

  • Anorchia (absence of testes)
  • Spermatogenesis disorders
  • Hypogonadism (poor gonadal development)
  • Radiation exposure, toxic, or infectious damage